Understanding the behavior of cementitious material under extreme loading is vital for the dynamic design of structures. In such conditions, deformations are confined, and compression is accompanied by pore closure of pores rather than cracking. This study analyzed pore structure changes in response to high oedometric compression of cement pastes. The effects of water-to-cement (w/c) ratio, saturation, and coating were investigated using mercury intrusion porosimetry (MIP). Compression decreased the porosity of all samples, but less so for saturated than unsaturated samples. Pore sizes of unsaturated samples were also reduced by compression, resulting in a narrow pore size distribution. Conversely, the compression of saturated samples resulted in a wider pore size distribution with a shift to larger pores due to the migration of water from smaller to larger pores under pressure. The effect of coating observed only at the highest w/c ratio may be associated with the decrease in permeability with the decrease in w/c ratio. Results were verified using residual volumetric strain values, demonstrating a good correlation with MIP measurements.

The accumulation of plastic waste presents serious environmental concerns. One promising approach to address this issue is to reuse plastic waste as aggregate in concrete, thereby reducing dependence on natural resources. However, incorporating plastic—such as recycled polypropylene (rPP)—into mortar and concrete presents challenges, primarily due to non-uniform particle distribution in the cementitious matrix. The density difference between plastic and the cementitious matrix causes rPP particles to migrate upward during casting, resulting in segregation and weakened upper layers. This study aims to minimize such segregation by enhancing the distribution of plastic particles within the mortar using viscosity-modifying admixtures (VMA), limestone powder (LS), and their combination. Mortar mixtures were produced with 25% of standard sand replaced by rPP, cast using CEM I 52.5R white cement, and compared to a reference mix without plastic. After curing, the cut cross-sections were analyzed using image processing to quantify the uniformity of rPP dispersion. Mechanical performance was assessed through compressive and flexural tensile strength tests at 7 and 28 days. The results indicate that LS filler significantly improved the distribution of rPP particles, reduced segregation, and enhanced mechanical properties in comparison to other rPP-containing mixes. These findings highlight the effectiveness of rheology modification strategies in improving the structural integrity and sustainability of plastic-modified mortar.

Durability governs the service life of reinforced concrete, yet practice often relies on accelerated tests whose results are not consistently established across mixtures. This study presents a single, side-by-side assessment of commonly used durability indices obtained by accelerated tests such as the chloride diffusion coefficient, the migration coefficient from the rapid chloride migration test, bulk electrical conductivity, charge passed in the rapid chloride permeability test, initial and secondary sorptivity, and accelerated carbonation measured on the same concretes made with four cement types and two water to cement ratios. A clear pattern emerges: migration and conductivity align most closely with the diffusion coefficient, reflecting their common dependence on pore connectivity, tortuosity, and degree of saturation. The rapid chloride permeability test, while convenient for screening, primarily reflects bulk electrical behavior and exhibits larger scatter and a weaker practical link to the diffusion coefficient, consistent with its sensitivity to pore-solution chemistry, specimen heating, and conditioning. This limits its use for quantitative design unless results are correlated to diffusivity and calibrated by binder family. Sorptivity and carbonation are not reliable predictors of the diffusion coefficient at the dataset level, but they remain essential for exposures governed by moisture cycling and carbon dioxide ingress and help interpret variability in durability properties other than diffusion. Binder composition systematically affects both magnitudes and correlations, while a lower water to cement ratio and increased curing age reduce conductivity and diffusion in a manner modulated by the reaction kinetics of supplementary cementitious materials. Overall, this work provides a binder-resolved, calibration-ready mapping from migration and conductivity to the diffusion coefficient within a single, consistent experimental framework to support performance-based service-life design.

Viscosity modifying agents (VMA) and superplasticizers (SP) are two common macromolecular admixture types for cementitious materials. VMAs are used to stabilize fresh cementitious materials, while SPs are used to disperse them. Most VMAs are bio-based polysaccharides that act in the water phase between particles; while most SPs are synthetic comb polymers, consisting of negatively charged backbones that help their adsorption to the cement particles' surface. The molecular structure of DNA contains elements of VMA – as it is a polysaccharide – and SP – as it is a polyanion. In this study, rheological measurements are used to compare how these three types of macromolecules (VMA, SP, and DNA) affect cementitious materials. It is found that DNA shows the combined effects of VMAs and SPs on cement paste: it lowers yield stress while at the same time maintaining or even increasing its viscosity, which permits reducing water content while avoiding bleeding or segregation of samples. Yet, the presence of DNA has a significant retardation impact on cement hydration, which is also a common side effect of VMAs and SPs.

Concrete waste fines (CWF) are a major by-product of concrete recycling. Recycled coarse aggregates have already been introduced into the construction industry. However, little has been done on the utilization of the fine fraction of concrete waste. This research investigated a method of recycling CWF to produce expanded lightweight aggregate (LWA) using gypsum as a foaming agent. Further, the effects of quartz and bauxite addition on the bloating characteristics of LWA were studied by utilizing the CWF by different ratios of 25, 36, 72, and 100%. This was done to modify the chemical composition of the mixture in accordance with Riley’s ternary diagram. A physical and chemical analysis of the raw materials was conducted initially using X-ray diffraction, and inductively coupled plasma spectroscopy. A series of tests were conducted with the burning temperatures and gypsum content as experimental variables. A detailed analysis of the apparent density, water absorption, and bloating index was conducted and the microstructure of LWA particles and pore sizes were studied using optical fluorescence microscopy. The experimental results demonstrated that adding 15% of gypsum by weight to the 25% CWF mixture and a maximum heating temperature of 1200 ℃, resulted in a bloating index of 155%, an apparent density of 573 kg/m³, and a water absorption of 128 wt. %. This expansion of LWA was achieved primarily due to the gypsum acting as a bloating agent. The research confirmed the feasibility of producing high-quality LWAs by combining fine concrete waste with gypsum.

Belite-based binders offer major advantages over Ordinary Portland Cement with high Alite content in terms of durability, low heat evolution, and low carbon footprint during production. To gain these advantages, activation of the most active polymorphs of Belite by the addition of mineralizers and rapid cooling is needed. However, the reaction rates and hydration products of pure Belite paste are still not well understood. This is due to factors such as i) the effect of mineralizers incorporated in Belite crystals on hydration; ii) the role of residual mineralizers left outside of Belite; iii) the effect of sulfate’s addition on Belite hydration. In this study, a clinker with a high content of α-Belite was prepared. The variable parameter was the amount of Gypsum added during the stage of cement preparation, which ranged from 0 to 30%. The results of the study confirmed that the reactivity of cement based on Belite is highly dependent on the content of sulfates. As sulfate content increases, the degree of hydration increases at an early age but decreases at later ages. It has also been found that Gypsum reacts during the Belite hydration and forms atypical new hydration products such as aluminate-free Ettringite and Apatite. The results of this research reveal a high potential for a new type of low-carbon binder system based on α-Belite with high Gypsum content.

The addition of bacterial biomass to cementitious materials can improve strength and permeability properties by altering the pore structure. Photoautotrophic bacteria are understudied mortar bio-additives that do not produce unwanted by-products compared to commonly studied ureolytic species. This study directly compares the impact of the addition of heterotrophic Bacillus subtilis to photoautotrophic Synechocystis sp. PCC6803 on mortar properties and microstructure. Cellulose fibers were used as a bacteria carrier. A commercial concrete healing agent composed of dormant bacterial spores was also tested. Strength, water absorption tests, mercury intrusion porosimetry, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy were applied to experimental mortar properties. The photoautotrophic modifications had a stronger positive impact on mortar strength and permeability properties than sporulated heterotrophic modifications due to differences in surface properties and production of exopolysaccharides. The findings provide support for photoautotrophic species as additives for mortars to move away from ammonia-generating species.

High intensity impact loading on a concrete structure induces three dimensional high intensity stresses, the analysis of which requires appropriate constitutive relationships describing the isotropic and deviatoric stress components. The isotropic component known as the hydrostatic relationship or the equation of state (EOS) is in the focus of this paper. The literature relates the EOS of concrete to its uniaxial compressive strength. This paper aims at refuting this relationship and validating the conjecture that the EOS depends on the concrete mixture. For that purpose, different concrete mixes of equal strength have been tested. The mixture parameters are the water content (with the same w/c ratio), the coarse aggregate content and the maximum aggregate size. Using a unique test setup, hydrostatic tests were carried out to extremely high pressures at the 1GPa level. The results clearly show the pronounced differences between EOS curves representing different mixtures having the same concrete strength, thus validating the above conjecture. As the EOS is sometimes derived from oedometric tests, the present investigation exploited oedometric tests results on exactly the same concrete mixtures and strength to compare the hydrostatic and oedometric resulted EOS curves. The comparisons show that for most cases the stress at a certain volumetric strain in the oedometric curves are somewhat lower than these in the hydrostatic EOS curves. However, for mixes with a large maximum aggregate size with a high aggregate content, the oedometric EOS merges with the hydrostatic EOS curves in the mid-to high pressure levels. Finally, statistical analysis using Analysis of Variance has been employed to identify the effect of different mixture parameters and their combination on the differences in the EOS. These new results enhance the insight on concrete behavior under triaxial high pressures and contribute to the development of a new generation of EOS curves.

The old hydrated cement paste in concrete waste is only partially hydrated. An efficient activation is required to liberate the unhydrated cement core surrounded by hydrates. This work innovated in the development of optimal mechanical activation techniques for recovering hydrated cement paste and using it as supplementary cementitious material in new mortar. The effect of recovered hydrated cement paste in the new mortar was compared to inert fillers, and a k-factor was calculated based on late compressive strength. The most efficient method for liberating the active cement core and activating the residual cementing properties was grinding in a planetary mill with a low concentration of grinding aids. Recovered cement fines reached higher compressive strength values than inert fillers and equivalent values to cement at later ages. The increment in compressive strength after 28 days indicated late hydraulic activity due to the high content of belite in the residual cement.

Internal curing is commonly implemented in concrete mixes with water-to-cement (w/c) ratios lower than 0.4 because of self-desiccation. Normal Strength Concrete (NSC) with w/c ratios higher than 0.5 would benefit from internal curing because of labor and resource-saving and quality control issues. However, the loss of curing water due to evaporation reduces internal curing efficiency in high w/c ratio mixes. This research evaluates a novel approach to minimizing internal curing water loss at an early age by combining internal curing with permeability-reducing admixtures (PRA) and shrinkage-reducing admixtures (SRA). Different mixtures containing binary and ternary combinations of admixtures and internal curing agents were investigated. According to the findings, admixtures such as SRA and PRA can play a vital role in maximizing the potential of internal curing in high w/c mixes. Furthermore, the ternary combination of LWA and the two admixtures has proven promising based on the observed overall improvement in NSC properties.

Autogenous curing, also known as internal curing (IC), has revolutionised the way high-performance concrete (HPC) and high-strength concrete (HSC) are cured. IC improves the service life of concrete by lowering early-age cracking and enhancing durability. However, normal-strength concrete (NSC), the most commonly used type in the industry, is typically cured using conventional methods. Researchers are thus looking at ways to reproduce the positive results found in internally cured HSC/HPC in NSC. Studies have shown that IC is feasible in NSC despite its higher permeability, which results in loss of internal curing water (ICW). However, no comprehensive study has attempted to assess how the type, size and amount of IC agents affect the properties of NSC. The aim of this work was thus to optimise IC parameters for autonomous curing of NSC. The findings of this study support the notion that IC is possible in concrete with a high water/cement ratio and that, compared with lightweight aggregates (LWAs), superabsorbent polymers significantly impacted the durability properties of the NSC. Moreover, varying the size of the IC agent (LWA) had little effect on NSC properties, while increasing the amount of ICW considerably improved the durability properties.

Belite-ye’elimite-ferrite (BYF) cements are considered an environmentally friendly alternative to ordinary Portland cement due to their lower carbon dioxide (CO₂) emissions and reduced energy requirements. However, their hydration mechanism and its effect on strength development have still to be clarified. Therefore, this study aimed to investigate the influence of gypsum contents on the hydration behavior and strength development of laboratory-prepared BYF cement. The studied cements were made from a clinker, produced at 1250 ℃, containing approximately 50% of belite (C₂S), 30% of ye’elimite (C₄A₃$), and 20% of ferrite (C₄AF) as the main phases. Phosphorus pentoxide and lithium oxide were added to the clinker to stabilize the α’_H-C₂S. The phase assemblage of the cement pastes was characterized by quantitative X-ray diffraction using Rietveld refinement at different ages. TGA and DSC methods were used to confirm the XRD data and to characterize the main amorphous hydrate phases. The hydration kinetics was studied using isothermal calorimetry for seven days. The strength development of BYF mortars with a water-to-cement ratio of 0.50 was studied for up to 56 days. The results showed that the optimal content of gypsum was 18 wt % due to the higher strengths at all ages and higher heat generation during hydration. Increasing the amount of gypsum increased the content of ettringite. In contrast, the content of strätlingite, the main hydration product of belite, decreased, and the content of unreacted belite in the cement increased. This indicates that the amount of gypsum strongly affects the hydration rate of belite.

There is no consensus on which hydration stoppage method is optimal to preserve the microstructure and mineral composition of samples, especially considering the specific aspects of different testing methods, such as TGA, MIP, or XRD. This paper presents a quantitative comparison between the most popular hydration stoppage strategies and parameters such as the sample piece size, the soaking time in a solvent, and the type, as examined on cement paste hydrated for 7 days. It was found that the carbonation appears either for samples smaller than 2.36 mm and bigger than 4.75 mm or samples soaked in a solvent for longer than 1 h. Fast solvent replacement leads to ettringite diminution and total pore volume increase. Among others, solvent replacement with subsequent gentle heating under a vacuum was found to be the most efficient, whereas it was experimentally demonstrated that isopropyl alcohol stops hydration faster than ethanol and acetone.

All types of concrete contain residual unhydrated cement. For example, unhydrated cement is present in high-strength concrete due to low water/cement ratios, as well as in old concrete due to coarser cement used in the past, and in fresh concrete waste due to the lack of curing. These residues of unhydrated cement are a waste of resources with potential for recovery and reuse. In this work, X-ray diffraction, thermogravimetric analysis, and analytical modeling were used to quantify the residual cement and the hydration degree of various cement pastes to explore their recovery potential. The study included cement pastes with water/cement ratios of 0.2–0.6 and residual unhydrated cement was found to be in the range 6–36%, indicating great potential for recovery and further use in the manufacture of new concrete.

One of the most important tasks in the investigation of hydrated cement paste is the determination of the amorphous phase content, which is mostly cementitious gel. The determination of the cementitious gel content is important for the evaluation of the hydration process. However, this task is not trivial and it is hard to achieve high accuracy. The major approach for determining the content of the amorphous phase is by the use of an internal or external standard in the x-ray diffraction (XRD) analysis. This study compared two external standards, as well as two procedures of internal standard intermixing on amorphous phase determination accuracy. In addition, a novel method of calibrating the HKL phase for the Partial Or Not Known Crystal Structure method of evaluation of the amorphous phase using an internal standard was applied and evaluated. For this purpose, cement pastes with water to cement ratios of 0.30, 0.35, and 0.40 were prepared, and hydration was stopped using the solvent exchange at the ages of 7 and 28 days. The hydrated cement paste samples were examined using XRD and the hydrates assemblage and amorphous phase content were analyzed using Rietveld refinement. The bound water in hydrated cement paste was studied using thermal analysis. For comparison, the degree of hydration was determined by XRD, thermal analysis, and isothermal calorimetry. The experimentally determined amorphous phase content was compared with theoretical calculations based on the degree of hydration and the recommendations for the best amorphous phase quantification procedure were given.

Many countries have resources of calcareous oil shale with low calorific value that are unsuitable for energy production. The chemical composition of calcareous oil shale is similar to that of Portland cement clinker. This study aimed to maximize the replacement of raw materials in clinker production with calcareous oil shale, while maintaining standard quality characteristics. Utilization of calcareous oil shale in raw state can partially replace both fuel and other raw materials. In this research, belite-rich Portland cement clinker was produced and studied in the laboratory. Grinding time and sulfate content were optimized and cement was prepared. The cement was investigated and its compliance with standard requirements was tested. We showed that oil shale can replace up to 76 % of raw materials in clinker manufacturing, which is sufficient for calcination and final burning in a rotary kiln. This means that oil shale can partially replace fuel, reducing CO₂ emissions during clinker production.

Concrete has the ability to heal cracks by its internal resources. In the work, a self-healing crack model has been developed. The model takes into account the cement content in concrete, the initial size distribution of cement particles, the degree of hydration, and the depth of hydration of individual cement grains. Assuming that unhydrated grains directly adjacent to the crack can participate in self-healing, the zone of influence of the crack and the potential for self-healing are evaluated. It was shown that the initial granulometric composition of cement, initial cement content, and degree of hydration at the time of cracking have a significant influence on self-healing potential.

BYF cements are a promising alternative to Portland cement due to their lower CO₂ emissions and energy demand. However, it is essential to assess how production parameters affect BYF clinker composition. In this study, clinkers with varying SO₃ content were synthesized at temperatures of 1100–1400 °C and retention times of 15–120 min. The mineralogy of the produced clinkers was analyzed using X-ray powder diffraction with Rietveld phase analysis. According to the results, firing temperatures of 1300–1350 °C, retention times of 30–60 min, and excess SO₃ are needed to obtain the desired clinker composition. It was proved that SO₃ contributed to the stabilization of β-C₂S and the formation of ye'elimite. Additionally, increasing SO₃ resulted in higher contents of cubic ye'elimite relative to orthorhombic. It was demonstrated that the level of Fe₂O₃ incorporated into C₄A₃$-c increased with the increase of SO_3, as indicated by the decrease in C₄AF and unit cell volume.

Even with the introduction of high-strength and high-performance concretes, normal strength concrete remains widely used in the construction industry. Curing concrete is a critical step and must be applied appropriately for any concrete structure to develop the desired mechanical and durability-related properties. External curing methods either provide extra water (water curing methods) or limit the loss of mixing water (sealed methods) from the mix, aiding the concrete to achieve the required properties. The experimental results have shown that 28 days of wet curing is the optimum curing approach, and to be considered acceptable, any curing method must produce concrete properties equivalent to 7-day wet curing. The NSC cured with curing compound did not produce results comparable to 7-day wet curing. Finally, external curing methods showed a strong correlation between water sorptivity and the threshold diameter; and the MIP test could be an effective curing quality assessment method in the field.

The recycling of concrete is essential because it reduces the environmental impact of concrete construction and demolition waste. For recycling, concrete waste is crushed and the coarse fraction of crushed material can be recycled as a coarse aggregate. Concrete waste fines, which are a mix of fine aggregates, coarse aggregate debris, and the hydrated cement paste, are currently not a part of the recycling process. Since hydrated cement paste has all the necessary chemical elements for clinker production but without heavy carbon dioxide emissions associated with traditional clinker raw material, it would be beneficial to recycle concrete fines for the production of clinker. However, the data available in the literature about the transformations of hydrated cement paste upon heating are contradictory. It is not clear whether hydrated cement paste can be converted back to clinker. In this research, the phase transformations in hydrated cement paste upon heating in the temperature range from 600 to 1450 °C were investigated using thermal analysis and X-ray diffractometry. The results show that hydrated Portland cement paste can be completely recovered into a new clinker using a thermal treatment. The main phase transformations during heating are described and compared to the literature data. The results indicate a great potential for the complete recycling of concrete fines for the production of cement with a low carbon footprint.

Recycling of concrete construction and demolition waste is necessary for the increase of sustainability and reducing the environmental impact of concrete construction because of the increasing rate of such waste production and its accumulation. Coarse aggregates can be partially recovered from concrete waste. However, it is not clear whether hydrated cement paste can be converted back to clinker. However, concrete waste fines, which are a mix of fine aggregates, coarse aggregate debris, and the hydrated cement paste, are currently not a part of the recycling process. The ability of hydrated cement paste to be recovered back to clinker minerals that have binder properties has not been studied systematically. In the current research, the phase transitions in hydrated cement paste heated to a temperature in the range from 600 and 1450 °C were investigated by means of X-ray diffractometry and thermal analysis. The experimental results demonstrate that hydrated Portland cement paste can be recovered back to clinker minerals. The recovered cement paste contains all the main clinker minerals similarly to the initial cement. The results provide evidence for the possibility of recycling hydrated cement and concrete into the cement clinker. The recycled clinker will potentially have a lower carbon footprint in comparison to original Portland cement.

The behavior of cementitious materials under severe loadings is of major importance for the security and protection of concrete structures. One of the key mechanical properties of materials subjected to extremely high loading is the relationship between the hydrostatic pressure and the volumetric strain, which is often referred to as the equation of state. In porous materials such as cement paste and mortar, this relationship is substantially inelastic due to the closure and collapse of capillary pores. The paper presents an enhanced theoretical model of the loading branch of the barotropic equation of state for cement paste, mortar, and concrete that utilizes non-linear bulk behavior of cement paste matrix and aggregates. A multi-scale approach is applied to simulate the bulk behavior of cement paste. At the micro-level, the model assumes that the Portland cement paste matrix has the same properties in any concrete or mortar, and the difference in bulk behavior is caused by the difference in pore structure and aggregates. In the presented model, we applied a four-stage equation of state comprising of a trilinear elastic-plastic behavior prior to the closure of the pores followed by a nonlinear Hugoniot-type behavior stage after the closure of the pores at high pressures. At the macro-scale level, the equation of state of the paste is obtained by averaging the micro-domains solutions. The equation of state for the aggregate material is described by the three-stage equation of state with bi-linear elastic-plastic behavior followed by nonlinear Hugoniot-type compaction for the high pressures range. The Hirsch phase mix rule is applied to obtain the equation of state of the composite concrete material. The proposed model allows prediction of the bulk behavior of cementitious composites based on its composition and properties of its components for a wide range of pressures up to extremely high pressures.

Oil shale is one of the largest energy resources today. Oil shales are horizontally layered rocks that have rich organic content called kerogen and mineral part is usually composed of clay.

In order to study the composition and microstructure of any hardening cementitious material, the ongoing hydration must be stopped [1]. At early hydration stages, the hydration stoppage is needed to suppress the further progress of hydration [2], allowing the analysis of several properties and characterization of the same sample at the same hydration age and therefore, at the same degree of hydration [3, 4].

The recycling of concrete can reduce the environmental impact of Portland cement production and concrete construction, and decrease the damping and landfilling of demolition waste. Currently, concrete recycling is widely used for aggregate extraction [1], though concrete fines which are a mix of aggregate and the hydrated cement paste are not a part of the recycling process [1]. Research efforts have been directed to the production of new Portland cement from recycled fines, but most research attempts run into problems [2, 3].

The efficiency of rail transport is crucial to compete with other transportation modes. Thus, over the years railway operators demand increasing rolling stock axle load and speeds. Hence, railway infrastructure improvements are crucial to withstand persistent increasing of bearing capacity expressed in significant dynamic load and cumulative traffic load.

Minimizing fluid transport properties of concrete is very important for providing prolonged durability of concrete structures. Sorptivity testing is an easy and effective method for evaluation of near-surface transport properties of concrete. In the sorptivity test, the moisture content of the tested sample has a dominating effect on the rate of absorption. Thus, the drying procedure during sample preparation is an important part of sorptivity testing. In the literature, many different procedures for sample preparation can be found, ranging from long room temperature drying to oven drying at 105 °C for 24 h. In this research, the effect of two drying procedures was compared: a milder one (ASTM C1585), and a more rigorous drying (DIN 52617). The comparison was performed on mortars with water to cement ratios of 0.35, 0.40, 0.45, and 0.50, as well as mortars at the water to binder ratio of 0.40 with different levels of cement replacement by fly ash and slag. The initial sorptivity obtained after these drying procedures was compared to chloride migration coefficient and conductivity test results, while the secondary sorptivity was compared with the total porosity. The latter procedure was found to give better correlations with other transport properties of mortars.

The article Application of ultrasonic pulse velocity for assessment of thermal expansion coefficient of concrete at early age, written by Semion Zhutovsky, Konstantin Kovler, was originally published Online without Open Access.

The behavior of cementitious materials under severe loading is of major importance for the security protection of concrete structures. One of the key mechanical properties of materials subjected to extremely high loading is the relationship between hydrostatic pressure and volumetric strain, which is often referred as the equation of state. In porous materials such as cement paste and mortar, this relationship is substantially inelastic due to the closure and collapse of capillary pores. At extremely high pressures, after all pores are closed, the equation of state approaches the elastic properties of the matrix. This paper presents an updated theoretical model of the equation of state of cement paste and mortar using a multi-scale approach. At the micro-scale level, an elastic-plastic spherical domain is considered with a single concetrical spherical cavity. The updated model includes a strain-hardening flow rule to describing the plastic closure of pores. At the macro-scale level, it is assumed that every differential spherical domain has random radial parameters following a realistic distribution function of pore sizes. The equations of state of the fine aggregates are assumed linear elastic and Hirsch phase mix rule is applied to obtain the equation of state of the composite material. All phases are assumed to be subjected to hydrostatic pressure. An extensive experimental study was conducted to calibrate and validate the proposed model. The comparison shows good agreement between the present model and the measured data.

The paper presents the development of an experimental setup to perform confined compression tests of cementitious paste, mortar, and concrete specimens at high pressures up to 1 GPa as well as the validation of the multi-scale model for the equation of state (EOS) of mortars. The test results for the EOS show that the secant bulk modulus of the loading branch monotonically increases with the content of fine aggregate. The comparison of the loading branches of the EOS for unsaturated specimens of two different specimen sizes indicates that there is negligible size effect for all types of the mixture compositions. Validation of the multi-scale model proposed previously for the EOS of a cement paste shows good agreement with the test results at the high-stress range with slight deviation at the lower stresses. It was demonstrated on mortars with a water to cement ratio of 0.50 that the Hirsch mixture model shows a good agreement with the test results for all levels of fine aggregate content in mortars.

Ternary binders have become used more frequently for several reasons. In some cases, such as combining a rapidly reactive SCM such as silica fume with a more slowly reactive SCM such as fly ash or slag, the use of ternary binders can provide benefits for both early-age and later-age properties and durability of concrete. In other cases, high-alkali pozzolans have been combined with slag to both accelerate the slag hydration and bind the alkalis from the pozzolan. As well, two SCMs may be combined to improve economy of the concrete mixture. This chapter describes properties of various ternary binders.

This paper aims at presenting the development of an experimental setup to perform confined compression tests of mortar and cement paste specimens at high pressures. The paper presents the effect of water/cement ratio (w/c) as well as the ratio of fine aggregate (sand) and its maximum grain size on the measured pressure – volumetric strain dependence (equation of state). Decrease of w/c ratio in a cement paste mix results in increase of the secant bulk modulus of the loading branch. The study includes unloading and reloading at different load levels. The bulk modulus of the reloading branch of a given composition depends almost linearly on the pressure magnitude. The secant bulk modulus (loading branch) of mortar specimens increases monotonically with the volumetric sand fraction. The experimental study shows a good repeatability of the different cement paste specimens and of specimens with fine sand; a relatively large scatter of the results is obtained for specimens with coarse sand. The developed damage was identified and recorded at the end of each test. In cement paste specimens cracks were identified only in the case of w/c = 0.50, while in the other specimens, no cracking was observed. In the mortar specimens with coarse sand, perpendicular cracks to the specimen axis were observed, while in the specimens, that contain fine sand, no damage has been indicated.

Sulfate attack can cause serious damage to concrete structures. Susceptibility of binders to chemical sulfate attack is often tested, however, no standard method exists for evaluation of concrete's resistance to physical sulfate attack. Traditional field testing of concrete's resistance to sulfate attack may take several years. Thus development of an accelerated testing procedure is required. The aim of this research is to evaluate suitable exposure conditions and deterioration evaluation methods suitable for accelerated testing. A number of methods for assessment of the level of deterioration were assessed. It was found that 100 thermal cycles between 5 and 30 °C while immersed in 30 wt% sodium sulfate solution were sufficient to assess the resistance of a wide range of mortar mixes. The mass loss proved as the most effective measure of the deterioration level.

Internal curing technology has been developed as a method for the reduction of autogenous shrinkage and cracking potential in high-performance concretes. The combination of autogenous and drying shrinkage, i.e. total shrinkage, of internally cured concrete is reported in the literature, almost unchanged after exposure to drying in a long term. On the other hand, the studied range of water to cement ratios is quite narrow. Accordingly, great interest aroused in the research of the effect of water to cement ratio on total shrinkage, as well as cracking potential of internally cured concrete. In this research, the restrained drying shrinkage of concrete with water to cement ratio of 0.33, 0.25 and 0.21, internally cured by means of water-saturated lightweight aggregate was studied. Strength, free drying shrinkage and mass loss of these concretes were also tested. The experimental results demonstrate that water to cement ratio has a considerable impact on cracking potential of internally cured concrete.

A new theoretical model for the equation of state (pressure–volumetric strain relationship, EOS) of cementitious composites is presented. The model employs a multi-scale approach and focuses on the loading branch of unsaturated cementitious composites like cement paste, mortar and concrete. The cementitious composite is a porous solid that combines the solid fractions of its constituents and capillary pores at different sizes filled in by air or partly by water. It is assumed that any contained water is fully drained during loading and it has no role in the compressibility process of the composite. Attention is given to the monotonic loading only, and unloading/reloading is not considered at this stage. The composite behavior under hydrostatic loading is described as a non-linear elastic-plastic material with hardening caused by the closure of the capillary pores. At the micro-scale level, a representative volume unit of an elastic-plastic spherical domain is considered to represent the solid material with a central single spherical cavity to represent the pore, while at the macro-scale level, it is assumed that every differential element has the properties of the above micro-level volume unit, where the interior and exterior boundaries radii are treated as random variables. The solid material is composed of cement particles and fine and coarse aggregates. The equations of state of the fine and coarse aggregates are assumed to be linear elastic. The phase mix rule is applied to account for the different mixture constituents and obtain the equation of state of the cementitious composite. The model is validated with available test results and good agreement is obtained. A parametric study of the model is performed to investigate the effect of mixture (cement paste and mortar) parameters on the shape of the equation of state.

Sulfate attack can cause severe damage to concrete structures. The most common mitigation strategy against chemical sulfate attack in concrete is reduction of water to cementitious materials ratio, use of low-C₃A Portland cements, and/or use of supplementary cementitious materials. However, physical salt attack from sodium sulfate exposure may still cause damage to concrete with low water to cementitious materials ratio, and supplementary cementitious materials have been reported to even reduce resistance to physical salt attack. The purpose of the current research is to study the effect of water to cementitious materials ratio and supplementary cementitious materials on the ability of mortar to resist physical salt attack. Mortars, made with water to cementitious materials ratios between 0.35 and 0.50, and with two levels of cement replacement by either fly ash or ground granulated blast-furnace slag, were exposed to physical sulfate attack. Mass loss due to physical sulfate salt attack and its relationship with pore structure and transport properties were studied. The results show a good correlation between the resistance to physical salt attack and the pore threshold radius using mercury intrusion porosimetry, as well as the chloride migration coefficient. For the curing conditions used, ground granulated blast-furnace slag was found to improve the resistance to physical salt attack, while fly ash demonstrated a negative effect.

Early age deformations, in concrete, may lead to cracking reducing its mechanical properties and service live. Cracking risk analysis is an essential part of a concrete design, and coefficient of thermal expansion of concrete is indispensable for this purpose. In this paper, an approach that utilizes ultrasonic pulse velocity measurements for assessment of thermal expansion coefficient of concrete at the early age is proposed. An expression for the calculation of the coefficient of thermal expansion was derived based on the theory of poromechanics. Free shrinkage and ultrasonic pulse velocity of cement paste with water to cement ratio of 0.33 were measured starting from the casting, in order to validate the formula. The calculated values were in an agreement with the data found in the literature, though the effect of self-desiccation was not captured. In addition, the calculated value of thermal expansion coefficient was used for decoupling of autogenous and thermal shrinkage of cement paste. Decoupled linear autogenous shrinkage was compared to the autogenous shrinkage measured by volumetric method.

The behavior of cementitious materials under severe loading is of particular interest, for research on ballistic impact, penetration and near distance explosions, where very high pressures are developed. Therefore it is important to investigate the behavior of such materials in the exceptionally high hydrostatic pressures range. One of the key characteristics of this behavior is the equation of state (EOS) that is the relationship between hydrostatic pressure and density (or bulk strain). However it has not been adequately investigated, and therefore the mechanisms of cementitious materials deformation and damage that are developed within that range of high pressures is at least partly obscure and far from being clearly understood. This is partly because the controlled application of extreme pressures requires special equipment and expensive experimental setups and testing is associated with a wide variety of technical problems. This paper aims at presentation of the development of an experimental setup to perform confined compression tests of mortar and concrete specimens at high pressures up to 1GPa. It presents the experimental study of different cement paste and mortar specimens and their comparison with previous results, obtained under high pressures up to 300 MPa. This allows the investigations of size effect for unsaturated samples, as well as the effect of the sand volumetric content on the loading branch of the equation of state. The experimental study shows a good repeatability for the cement paste specimens and for mortar specimens with fine sand. It also shows that decrease of water/cement ratio in the cement paste mix as well as increase of the sand volumetric contain in mortar results in monotonic increase of the secant bulk modulus of the loading branch of EOS. The comparison of the mean loading branch of the experimental EOS for unsaturated specimens having 30 mm diameter (70 mm height) and 70 mm diameter (150 mm height) clearly indicates that there is practically no size effect for all tested mixture compositions. While for the cement paste there is no difference up to 270 MPa (highest pressure level in the test in the small apparatus), the addition of sand yields an increase of the difference, which, anyway, remains small.

The behavior of concrete under severe loading is of interest, especially for problems like ballistic impact and penetration and near distance explosions, where very high pressures are developed. For these problems the behavior of concrete at very high hydrostatic pressures is of importance. There is very little data available on concrete behavior at that high pressure level. Therefore there is much need for an extensive experimental work in order to provide necessary data and illuminate the rather obscure area of concrete behavior at high pressures. However high pressure controlled testing requires special and expensive equipment, and the testing is associated with a wide variety of technical problems. Recently published experimental data, obtained by utilizing a high-capacity tri-axial press, indicates that concrete that is subjected to high pressures behaves differently than concrete under low uniaxial loading. When uniaxial loading is applied, without any confining pressure, the concrete specimen demonstrates a well-known brittle behavior where failure is caused by a localized damage. Quite to the contrary, at high levels of confining pressures, the concrete behaves like a ductile material, and its failure is associated with diffuse material damage. The experimental data at the very high pressure range is most important to understand the processes of damage evolution that governs the characteristics of the equation of state. This paper presents the development of an experimental setup that is capable of performing confined compression tests of mortar and concrete specimens at high pressures up to 400MPa. The experimental study aims at investigating the effect of water/cement ratio as well as the ratio of fine aggregate on the different branches of the equation of state: active loading and unloading/reloading. The paper presents some of the test results as well as a new equation of state that is based on the multi scale approach. The model is applicable for dry materials; cementitious paste and concrete in which the pores are filled with water should be treated differently to account for the liquid phase.

Physical sulfate salt attack is one of the most rapid and severe deterioration mechanisms in concrete structures. One of the most common approaches to improve resistance of concrcte to sulfate attack is to use supplementary cementitious materials However, physical salt attack may still cause damage to concrete with supplementary cementitious materials. Moreover, according to some literature sources, some supplementary cementitious materials may even reduce resistance to physical salt attack. The current research investigates the effect of supplementary cementitious materials on the ability of mortars to resist physical sulfate salt attack and its relationship with pore structure and transport properties. Mortar specimens with 45 and 65% replacement of cement by ground-granulated blast-furnace slag and with 20 and 40% replacement of cement by fly ash were exposed to physical sulfate attack. The results show a good correlation between the pore microstructure and transport properties to the resistance to physical salt attack. Ground-granulated blast-fiirnace slag was found to improve the resistance to physical salt attack, while fly ash demonstrated a negative effect.

The paper focuses on cementitious composites including concrete that are subjected to exterior hydrostatic pressure. The hardened cementitious composite is amultiphase material, containing cement paste, sand, water and air voids. A concrete composite contains coarse aggregates as well. The present paper presents an attempt to theoretically derive the equation of state of a hardened cementitious composite using a multi-scale approach. The equation of state represents the non-linear elastic-plastic behavior with hardening that is required to describe the volume change with increasing hydrostatic pressure on a representative specimen of the material. At sufficiently high pressures, it includes the closure of capillary pores. At the micro-scale level, an elastic-plastic spherical domain is considered with a single spherical cavity, while at the macro-scale levelit isassumed that every differential spherical domain has random radial parameters following a log-normal cumulative distribution function. The equations of state of the fine and coarse aggregates are assumed linear elastic. The phase mix rule (parallel model) is applied to obtain the equation of state of the entirecomposite material. All phases are assumed to be subjected to hydrostatic pressure.The proposed model is compared to available test data on mortar for validation and the comparison shows good agreement betweenthe proposed model prediction and the experimental results.

Coefficient of thermal expansion of concrete is an essential part of cracking risk analysis. A formula for coefficient of thermal expansion based on the theory of poromechanics was derived. This formula utilizes ultrasonic pulse velocity measurements. To validate the formula, ultrasonic pulse velocity and free shrinkage of cement paste with water to cement ratio of 0.33 were measured starting from the casting. A good agreement was found between the calculated values and the data found in the literature. In addition, the calculated coefficient of thermal expansion was applied for decoupling of thermal and autogenous shrinkage of cement paste. Decoupled linear autogenous shrinkage was compared to the measured volumetric autogenous shrinkage.

The article presents the results of a round-robin test performed by 13 international research groups (representing fifteen institutions) in the framework of the activities of the RILEM Technical Committee 225-SAP "Applications of Superabsorbent Polymers in Concrete Construction". Two commercially available SAP materials were used for internal curing of a high-performance, fine-grained concrete in combination with the addition of extra water. The concrete had the same mix composition in all laboratories involved but was composed of local materials. All found a considerable decrease in autogenous shrinkage attributable to internal curing. Also, with regard to the shrinkage-mitigating effect of both particular SAP materials, the results were consistent. This demonstrates that internal curing using SAP is a robust approach, working independently of some variations in the concretes' raw materials, production process, or measuring technique. Furthermore, the effects of internal curing on other properties of concrete in its fresh and hardened states were investigated. These are consistent as well and expand considerably the existing data basis on properties of concrete materials containing SAP.

Curing plays an essential role in the modern concrete technology, since it has a crucial effect on the development of concrete properties. High-performance cementitious systems are especially sensitive to the applied curing methods because of self-desiccation and high sensitivity to early-age cracking. Thus, it is of particular interest to compare the efficiency of internal curing and traditional curing techniques such as sealing and water ponding. In this study, the efficiency of different types of curing was estimated by means of isothermal calorimetry. Four different water to cement (w/c) ratios in the range of 0.21-0.45 and four types of curing were studied, including sealing, water ponding with different amount of water, internal curing by saturated lightweight aggregate and super-absorbent polymer. The hydration degree was determined using heat of hydration data. Compressive strength of the tested specimens was measured and analyzed. The results indicate that efficiency of different types of curing strongly depends on w/c ratio.

Internal curing technology has been developed to counteract autogenous shrinkage of high-performance concrete. However, the total shrinkage of internally cured concrete is reported to be almost unchanged after exposure to drying. On the other hand, shrinkage reducing admixtures have been successfully used to reduce drying shrinkage. A hybrid curing technique that combines internal curing with shrinkage reducing admixture seems to be a promising approach for reduction of total shrinkage and cracking potential of high-performance concrete. Ring test of concrete made at water to cement ratio of 0.33 and internally cured by water-saturated lightweight aggregate and super-absorbent polymer and their combination with shrinkage reducing agent was studied. In parallel, compressive and splitting strength, drying shrinkage and mass loss of the same concrete mixes were measured. The results demonstrate the synergy between internal curing and shrinkage reducing admixture resulting in a marked reduction of cracking potential.

The paper "Super absorbing polymers as an internal curing agent for mitigation of early-age cracking of high-performance concrete bridge decks" deals with different aspects of using superabsorbent polymers (SAP) in concrete to mitigate self-desiccation. The paper concludes that "Addition of SAP leads to a significant reduction of mechanical strength". The experimental results are in contradiction with several publications and question the appropriateness of using SAP as internal curing agent. However, the observed strength loss - and possibly also other observations - seems to be caused by overestimation of SAP water absorption. This results in an increase in water/cement ratio (w/c) for concrete with SAP. It is misleading to conclude on how SAP influences concrete properties, based on comparison of concrete mixes with SAP and reference concrete without SAP, if SAP mixes have higher w/c than the reference mix.

Internal curing technology has been developing to counteract autogenous shrinkage of High-Strength (HSC)/High-Performance (HPC) Concrete. However, by introducing weak porous material as the internal water reservoirs, strength and durability properties can be downgraded. On the other hand, cracking due to autogenous shrinkage has extensively detrimental effect on concrete durability. Thus, when durability of HSC/HPC is considered, transport properties have to be viewed in the bundle with the risk of cracking. Research on durability of internally cured concretes in general, and durability of internally cured concretes with very low water to cement ratios in particular, attracts much interest, since very little information is available in the literature in this regard. The paper reviews the existing publications in the topic. The cracking sensitivity of concrete made at water to cement ratios of 0.21 to 0.33 and internally cured by means of water-saturated lightweight aggregate of volcanic origin (pumice) was studied in this research. In parallel, resistance to chloride penetration, air permeability and sorptivity of the same concrete mixes was tested. The experimental results demonstrate that internal curing efficiency in reducing cracking sensitivity of concrete increases with the reduction of water/cement ratio, while transport-related properties of concrete are improved, or at least as good as, those of the reference concrete.

Internal curing of high performance concrete (HPC) by pre-saturated lightweight aggregates is a well-established method of counteracting self-desiccation and autogenous shrinkage. However, by introducing the internal water reservoirs strength and durability properties can be injured. Tests by the widely accepted methods of durability assessment, such as resistance to chloride penetration, air permeability, water absorption, autogenous and drying shrinkage and mass loss, were conducted on HPC mixes made at water to cement ratios in the range of 0.21-0.33. The effect of internal curing on the durability related properties of high-performance concretes as a function of water to cement ratio is reported.

The present paper presents a systematic evaluation of cracking sensitivity, addressing the major parameters in concrete technology, especially for the high end of concrete quality. The variables studied were w/c ratio in the range of 0.29 to 0.45, cement content, type of cement (CEM I, CEMII and CEMIII), and the type of mineral additive added to the concrete (fly ash, metakaolin and microsilica). The performance of the concretes was evaluated by determining free shrinkage and weight loss upon drying, development of compressive strength, and characterization of cracking using the ASTM C 1581 ring test. Classification of the various parameters with regards to cracking sensitivity was performed based on the ASTM criteria and also on a more advanced one which was developed by the authors. The influence of the various variables was discussed in terms of the development of the whole array of the basic properties.

Internal curing of high-strength concrete has been the subject of extensive research for the last decade. The concept of protected paste volume has been one of the most significant theoretical approaches to internal curing. In this paper, the applicability of the protected paste volume concept to internal curing is re-evaluated in view of recent experimental evidence. It is shown, that the concept of protected paste volume and recommendation to limit the spacing factor to approximately 200 μm, cannot be extended to internal curing of high-strength concrete, since the distance of penetration of the internal curing water into the surrounding matrix depends mainly on the availability of internal curing water to the surrounding cementitious matrix. The pore structure of LWA and the size of SAP particles seem to have a marked influence on the availability of internal curing water and thus are factors of greater importance than the spacing factor.

Non-structural cracking of concrete is a serious problem and the underlying phenomena, namely, shrinkage and creep, need to be better understood. Much research has been devoted to this complex problem. However, despite major successes, the phenomenon of shrinkage is still far from being fully understood. The paper discusses the main aspects of concrete shrinkage, with a focus on autogenous and drying shrinkage, which are especially important in high-strength and normal-strength concretes, respectively. These aspects include the theories of physical mechanism, prediction models and future research trends. Shrinkage of concrete due to (a) moisture changes, which result in surface and capillary tension, movement of interlayer water and disjoining pressure and (b) chemical reactions (hydration/dehydration shrinkage, thermal shrinkage, crystallization swelling, carbonation shrinkage and phase transition shrinkage, is reviewed. Many of these mechanisms often cannot be directly linked to the macroscopically observed dilatation/contraction. In some case, volume changes due to chemical reactions influence porosity and degree of saturation. Most chemically induced volume changes are affected by temperature, since chemical reactions are generally accelerated by the temperature elevation and slowed down by the temperature reduction. An overview of recent model devel opments is presented. Shrinkage reduction methods (cement modification, using admixtures and fibers, proper mix design, methods of internal curing) are discussed.

A novel approach to has been recently proposed mitigate self-desiccation, one of the foremost problems of high-performance concrete (HPC). It is based on incorporation of pre-soaked lightweight aggregate in the concrete mix. Such aggregate acts as an internal water reservoir preventing reduction of relative humidity in the cementitious matrix. This method is known as "autogenous" or "internal" curing. Recent studies demonstrated that this kind of curing could be successfully applied to obtain improved HPC with reduced sensitivity to cracking. However, the content of lightweight aggregate required to completely eliminate autogenous shrinkage was high, and this caused a reduction of compressive strength and an increase in the cost of the concrete. Recently, a work has been conducted to optimize the internal curing strategy by eliminating autogenous shrinkage while using the smallest possible amount of lightweight aggregate. The effect of grain size, pore structure and type of the lightweight aggregate was studied. The next step in this study - the effect of the properties of the cement paste matrix on the effectiveness of internal curing is discussed in this paper.

Synopsis: The paper deals with internal curing of High-Strength Concrete using presoaked lightweight aggregate (LWA). The effect of internal curing depends directly on the distance over which the internal curing water can travel. The effectiveness of internal curing is a function of the ratio between the water penetration depth and the paste-lightweight aggregate proximity, which is related to the spacing between the aggregates. Estimates of these parameters were developed in this study, based on a combination of modeling and experimental work. The results indicate that water can penetrate from the LWA into the surrounding matrix to a distance of up to several millimeters during the first seven days of hydration. The water penetration was sensitive to the pore structure of the aggregate, ranging from about 1 to 6 mm, and it was reduced in systems having lower w/b ratio and silica fume by almost a factor of 2.

High Strength Concretes (HSC) with extremely low water to binder (w/b) ratios are characterized by high cracking sensitivity which is a consequence of increased autogenous shrinkage. The major reason for autogenous shrinkage - self-desiccation - cannot be eliminated by traditional curing methods. The application of the concept of internal curing by means of saturated lightweight aggregate was applied and shown to be effective in eliminating autogenous shrinkage. The present paper describes an approach to optimize the size and porosity of the light-weight aggregate to obtain effective internal curing with a minimum content of such aggregate.