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One of the perspective approaches for converting natural and technogenic mineral sources into eco-friendly cementitious materials and composites is through alkali activation technology. Over the past few decades, an extensive resource base of mineral sources has been established for alkali-activated materials (AAMs). This resource base is continuously expanding with the rapid development of alkali-activation theory and technology, as well as ongoing studies by numerous research groups around the world. In addition, the sustainable development and circularity paradigm, which aims for a "zero-waste" future, has heightened the importance of focusing on the upcycling of large-tonnage wastes, such as construction and demolition wastes, including concrete wastes (CWs). The challenges associated with effectively upcycling CWs through geopolymerization technology, including diverse chemical-mineralogical compositions, factors influencing suitability as a sole or complementary precursor, and approaches to maximize recycling value, are discussed in this review. It is suggested to categorize CWs as high- and low-Ca types. Further research should be conducted to determine optimal composition criteria, techniques to enhance reactivity, establish durability aspects, and reduce alkaline activator content. These efforts would greatly contribute to advancing the raw material base, reducing production process complexity and costs, and enhancing both the environmental and economic potential of CW-based geopolymers. • Concrete wastes are promising precursors for alkali-activated materials. • Concrete wastes should be categorized as high- and low-calcium precursors. • Polymerization activity increases proportionally to cement paste/aggregates ratio. • Activation techniques make concrete wastes more resilient for the future. [ABSTRACT FROM AUTHOR]

• Time-dependent rheological behavior after continuously shearing was investigated. • A parameter describing the disappearance of shear thinning at down curve was proposed. • Physical and chemical properties affect the evolutions of rheological properties with shearing. Shear history exerts a great impact on the rheological properties, and thus the consolidation and construction quality of concrete. This study experimentally investigated the time-dependent rheological behavior of cementitious pastes under continuously shear mixing. A parameter describing the disappearance of shear thinning at the decelerating curve was proposed. Results indicate that continuous shear mixing could not effectively hinder the development and evolution of thixotropy and yield stress of cementitious pastes over time. After continuously shear mixing for a while, the critical shear rate corresponding to the disappearance of shear thinning increased. Cementitious pastes tended to exhibit shear thinning behavior at relatively lower shear rate ranges. At higher shear rates, the rheological behavior of cementitious pastes after continuously shearing was strongly dependent on the composition of cementitious materials. The evolutions of rheological properties after continuously shearing were associated with the physical nature and chemical hydration of cementitious pastes. [ABSTRACT FROM AUTHOR]

• The influence factors on chloride binding of AACs are studied. • The Langmuir isotherm suits better for chloride adsorption of most of AACs. • The chloride binding is predominantly affected by the chloride concentration. • The Friedel's salt only presents in AAS samples after adsorption equilibrium. • The bound chloride of AACs increases with the increased w/b ratio. In this study, the effects of slag/fly ash ratio, Na 2 O concentration, silicate modulus of activators and water/binder ratio on chloride binding of alkali-activated slag/fly ash cements (AACs) are studied, using the binding isotherms. The Langmuir isotherm suits better for chloride adsorption of most of AACs, and the amount of bound chloride is predominantly influenced by the chloride concentration. The Friedel's salt only presents in alkali-activated slag samples after adsorption equilibrium. An appropriate slag/fly ash ratio could improve the chloride binding capacity due to the physical adsorption of N-A-S-H. The chloride binding of AACs decreases with the increased Na 2 O concentration but increases with the increased water/binder ratio, which is believed to be related to the OH− concentration in pore solutions. [ABSTRACT FROM AUTHOR]

• The effects of silicate modulus (Ms) on carbonation of AACs are studied. • The carbonation rate and the amount of CaCO 3 decrease with the increase of Ms. • The carbonation behaviors of high-Ca systems are different from the low-Ca systems. In this study, the effects of silicate modulus of activators (Ms) on carbonation of alkali-activated slag/fly ash cements are studied and compared between natural (0.03–0.04% CO 2) and accelerated (1% CO 2) carbonation conditions, via XRD, FTIR and TG/DTG techniques. Carbonation results in the decalcification of the C-A-S-H gels and the formation of calcium carbonates and silica gels, while the N-A-S-H gels are essentially constant after carbonation. The main calcium carbonate phase after carbonation is calcite, and the increase of Ms leads to the generation of vaterite and aragonite. The carbonation behaviors of low-calcium system (20% slag) are different from the high-Ca systems (100% and 60% slag), while the carbonation rate and the amount of calcium carbonates generally decrease with the increase of Ms in all of the studied systems. This investigation provides an in-depth understanding of carbonation mechanisms of alkali-activated cements, and is essential for the establishment of carbonation models and prediction of long-term performances. [ABSTRACT FROM AUTHOR]

Highlights • Pretreated LWA provided more internal curing water than dry LWA. • Pretreated LWA was beneficial for hydration of SCMs. • Pretreated LWA reduced total porosity and enhanced the microstructure. • 10-15% content of pretreated fine LWA is recommended for UHSC. Abstract In this paper, effects of fine lightweight aggregate (LWA) contents and their pretreatment methods on mechanical performance, shrinkage and pore structure of ultra-high strength concrete (UHSC) were investigated. Two pretreatment methods, namely, normal soaking and vacuum saturation were applied to study their effect on internal curing performance of LWAs as compared with un-treated LWAs. In general, the pretreated fine LWA effectively enhanced the flexural strength of UHSC specimens especially at later ages, while no significant improvement was observed for the compressive strength. Pretreated fine LWA using normal soaking and vacuum saturation provided internal curing water for progressive hydration, and enhanced the microstructure at the interface of LWA and the bulk paste. The pretreated fine LWA reduced the autogenous and drying shrinkage. The maximum efficiency was obtained when 10 to 15% fine LWA was used. Pretreated fine LWA under the vacuum condition was the most effective method. This method helped to maintain the internal RH of UHSC for a longer period and decreased the mass loss by reducing the total porosity of the UHSC. [ABSTRACT FROM AUTHOR]

Highlights • The physical and chemical effects of limestone powder (LP) were calculated. • The chemical effect of LP was influenced by its particle size and amount of LP at 3d. • The particle size and amount of LP had little effect on its chemical effect at 180d. Abstract The study aims to quantitatively calculate the physical and chemical effects of limestone powder (LP) with four average particle sizes and two amounts in cement pastes by using thermal gravimetric analysis (TGA), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) techniques. At 3d, as the average particle size of LP decreased from 32 to 6 μm, the consumed CaCO 3 content in LP increased from 0.67% to 1.71%, and the chemically reactive portion of LP increased from 1.15% to 2.95%. However, at 180d, the consumed CaCO 3 content and chemically reactive portion of LP was almost 2.4% and 4.2%, respectively. At 3d, as the LP content increased from 25% to 50%, the consumed CaCO 3 content in LP increased from 1.71% to 2.02%, and the chemically reactive portion of LP increased from 2.95% to 3.5%. However, at 180d, the differences of consumed CaCO 3 content and chemically reactive portion of LP between cement pastes with different LP content were limited. The physical and chemical effects of limestone powder on the compressive strength of cement pastes were calculated. At 180d, as the average particle size of LP decreased from 32 to 6 μm, the contribution of chemical effect of LP on the compressive strength of cement pastes increased from 1.01% to 1.08% while the contribution of physical effect decreased from 21.19% to 20.03%. [ABSTRACT FROM AUTHOR]

Highlights • Effects of rotational shearing on rheology of mortars with glass fiber are investigated. • The shear-induced behavior of mortar with glass fiber depends on the matrix composition. • Fresh mortars with glass fibers easily exhibit shear-thickening behavior. Abstract Shear stresses are always applied to fresh concrete during mixing and transporting processes, which have significant influences on the dispersion and agglomeration of cement particles. In this study, the effects of rotational shear mixing on rheological properties of fresh short glass fiber reinforced mortars with different mineral admixtures (containing fly ash and silica fume) were experimentally investigated. The shear rates of 50 s−1, 100 s−1 and 150 s−1 were selected as the rotational shearing rates. The Herschel-Bulkley model was used to characterize the rheological behavior of fresh glass fiber reinforced mortar. Results showed that the shear-thickening intensity increased with the increase of glass fiber volume fraction for the cement-fly ash binary mortar, while the addition of glass fiber resulted in the rheological behavior of cement-silica fume binary mortar changed from shear-thickening to shear-thinning response. After subjecting to rotational shear mixing, the measured shear stress was significantly increased and the fresh mortars with glass fibers easily showed shear-thickening behavior. [ABSTRACT FROM AUTHOR]

Highlights • The effects of limestone powder (LS) depends on its particle size and content. • Using LS to replace fine aggregate improves the properties of concrete. • Using LS to replace cement reduces the properties of the concrete. Abstract Limestone powder (LS) is one of the mineral materials in concrete due to its wide availability and low cost. This paper discusses effects of LS on the workability, setting time, shrinkage, mechanical properties and durability of concrete. Such effects are mainly influenced by many factors, including the particle size and content of LS, the polymorph of calcium carbonate and synergetic effect between LS and alumina-rich supplementary cementitious materials (SCMs). In general, incorporating LS, as cement paste replacement or in the form of fine aggregate, improves the properties of concrete. Whereas, when LS is incorporated into concrete to replace cement, effects of LS on the properties of concrete depend on its particle size and content. In the end, some further research needs are also suggested. [ABSTRACT FROM AUTHOR]

Highlights • A novel low-calcium clinker with C 3 S 2 and γ-C 2 S was synthesized at low string temperature. • The low-calcium clinker reduces the CO 2 emission and energy consumption. • The low-calcium clinker can obtain a higher strength through CO 2 curing. Abstract Portland cement clinker contains more than 50% tri-calcium silicate (C 3 S) and is produced at ∼ 1450 °C, which releases about 850 kg CO 2 per ton of clinker. Therefore, the use of dicalcium silicate (C 2 S) or rankinite (C 3 S 2) in cement can be an alternative to reduce CO 2 emission due to their low-calcium. In the present study, a novel low-calcium clinker containing C 3 S 2 -γ-C 2 S-C 2 AS (Ca 2 Al 2 SiO 7) was synthesized, then the clinker was under carbonation curing. Experimental results show that the low-calcium clinker was synthesized at sintering temperature of 1320 °C, lower 130 °C than that of Portland cement. The clinker with non-hydraulic phases can be fully harden within 24 h and obtain a higher compressive strength. The mainly carbonation products of the clinker were calcite, aragonite and polymerization silica gels, which was attributed to the compressive strength development. In addition, calcium hydroxide and C-S-H were not detected due to the non-hydraulicity properties of C 3 S 2 and γ-C 2 S. The carbonated clinker samples displayed a denser microstructure and lower pore structure. This study shows that the low-calcium and low sintering temperature clinker can obtain a better performance through carbonation curing. [ABSTRACT FROM AUTHOR]

Highlights • The rheological behavior of cement paste under continuous mixing was investigated. • High-rate shear mixing or adding fly ash slowed down the evolution of thixotropy. • An effective way to hinder the evolution of flocculation structure was proposed. Abstract The shear rate experienced by the cement pastes inside fresh concrete depends on the placing operations and the nature of concrete, and it plays an important role in the evolution of rheological properties and stability of fresh concrete over time. In this study, the effects of continuous shear mixing and fly ash on thixotropy, apparent viscosity, and shear-thickening behavior of cement pastes were experimentally investigated. Various shear rates of 1 s−1, 15 s−1 and 30 s−1 were selected to continuously shear the cement pastes. Results showed that the action of high-rate shear mixing slowed down the evolution of thixotropy, but the efficiency of reduction was gradually limited. Under the state of continuous shear mixing, the apparent viscosity of reference paste was significantly increased and the shear-thickening intensity at higher shear rate range was decreased. However, for the cement pastes containing fly ash, only slight increase in apparent viscosity was observed and the shear-thickening intensity also exhibited a slight increase behavior. It would be an effective way to hinder the evolution of flocculation structure by exerting a continuous shear mixing at an appropriate shearing rate and adding fly ash. [ABSTRACT FROM AUTHOR]

Highlights • Use CO 2 to treat harden cement powder as a supplemental cementitious material. • The incorporation of carbonated cement powder enhances the compressive strength. • Replacement of cement with carbonated cement powder shows a denser microstructure. Abstract Recovering aggregates from recycled concrete produces a large amount of powder, which contains hardened cement paste and is classified as a corrosive hazardous material. This study used CO 2 to treat hardened cement paste powder and to investigate how the incorporation of uncarbonated and carbonated hardened cement paste powder into cement affects the hydration and microstructure development of cement. Carbonated hardened cement paste powder consists mainly of calcite and silica gel. Replacement of cement by uncarbonated cement paste powder content from 10 to 30% by the mass of cement decreases, while replacement of cement with 10–20% carbonated hardened cement paste powder increases the strength of cement up to 90 days. The replacement of cement with 30% carbonated waste paste powder slightly decrease the strength of the cement. The silica gel in carbonated hardened cement paste powder quickly reacts with calcium hydroxide and results in the formation of more C-S-H. The presence of calcite in carbonated hardened paste powder leads to the formation of calcium aluminate hemi-carbonate (CAHC) and calcium aluminate mono-carbonate (CAMC) thus to a stabilization of ettringite (AFt) compared with the control cement paste, in which portion of AFt converts to mono-sulphoaluminate. CAHC is less stable than CAMC and transforms to CAMC in about one week after its formation. These chemical actions lead to a lower porosity and a higher compressive strength for cement paste with carbonated hardened paste powder compared with the control cement paste. [ABSTRACT FROM AUTHOR]

In this paper, fiber-matrix interfacial bond and static and dynamic mechanical properties of non-fibrous UHPC matrix and UHPC containing 2% steel fibers made with different types of supplementary cementitious materials (SCMs) and nano-particles were investigated. A mixture containing 20% silica fume, by mass of binder, was used as a reference. Five other mixtures prepared with 20% silica fume as well as 20% fly ash, 20% slag, combination of 20% fly ash and 20% slag, 3.2% nano-CaCO 3 , or 1% nano-SiO 2 were also investigated. The drop weight impact testing method was used to evaluate the impact flexural properties. The static flexural behavior was also investigated using specimens with the same size. Mercury intrusion porosimetry (MIP) was used to examine the microstructure of the matrix. Test results indicated that the incorporation of 20% silica fume in addition to either SCMs or nano-particles resulted in improvement in fiber-matrix bond and mechanical properties of UHPC. This can be attributed to the optimization of hydration products and densification of microstructure. The highest fiber-matrix bond and flexural strengths were found in the UHPC mixture containing 20% slag or 3.2% nano-CaCO 3 . Their 28d fiber-matrix bonds were increased by 30%–48% compared to the reference mixture, while 20%–30% greater for the 7d impact flexural strength. Therefore, slag and nano-CaCO 3 are recommended for enhancing the flexural properties of UHPC. [ABSTRACT FROM AUTHOR]

Limestone powder (LS) has been widely used in cement-based materials; and reportedly, can influence their properties by filler, nucleation, dilution and chemical effects. The action mechanism of LS mainly depends on its particle size and amount. The filler effect of LS refines the microstructure and reduces the porosity of cement-based materials. Its nucleation effect accelerates the hydration of C 3 S, increases the amount of hydration products and reduces the porosity of cement-based materials at early ages. Its dilution effect reduces the hydration peak of C 3 S, decreases the amount of hydration products and increases the porosity of cement-based materials. Its chemical effect promotes the appearance of third hydration peak, forms carboaluminate and reduces the porosity of cement-based materials. [ABSTRACT FROM AUTHOR]

Proper mixture design of concrete is of great significance for the quality of the concrete materials and structures. For #2 Dongting Lake Bridge in China, several performance requirements were required for designed concrete mixtures, including compressive strength, drying shrinkage, cracking resistance, alkali-aggregate reaction, permeability, and carbonation resistance. In this study, a mixture design method of concrete with multiple performance requirements was used to design C55 concrete for the project. The relationships between cement-fly ash-slag ternary cementitious composition and different properties were established based on the seven-batch factorial design method. Based on the requirements for different properties, a composition range meeting all requirements could be obtained. The verification tests showed that the designed mixture was suitable for the construction of #2 Dongting Lake Bridge. [ABSTRACT FROM AUTHOR]

Many of the degradation problems of concrete can be attributed to the weak surface layer. Surface treatment of concrete has been proven a simple and effective method to enhance the durability of concrete. In the present study, two series of portland cement mortar specimens with w/c ratios of 0.4 and 0.3 were prepared. CO 2 treatment was applied to he mortars 24 h after casting. The results indicated that CO 2 treatment resulted a carbonated a layer of less than 1.6 mm in thickness, slightly increased compressive strength, but significantly reduced the water permeability, water-vapor transmission and chloride migration of the mortars. Environmental Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR) Spectroscopy and thermogravimetric analysis (TGA) results indicated that calcium silicate hydrate with low Ca/Si ratio and CaCO 3 were the products in the carbonated surface layer. [ABSTRACT FROM AUTHOR]

This study investigated the early age autogenous and chemical shrinkage of mortars with slag and fly ash obtained by sieving the freshly mixed concrete after mixing. The hydration heat and contents of air voids formed within mortars during cement hydration were also tested using isothermal calorimetry and 1 H NMR. The results showed that the decrease of w/b ratio significantly increased the autogenous shrinkage of mortars, which was more significant for the mortars containing fly ash and slag. With the increase of slag and fly ash replacement level, the autogenous shrinkage of cement mortars decreased linearly. At the same w/b ratio the cumulative heat of hydration and autogenous shrinkage of cement pastes have a good linear correlation. The fraction of voids formed during hydration increased significantly with increasing w/b ratio. For samples with high w/b ratio (e.g. 0.4), the volume of air voids was higher than that of autogenous shrinkage, which was lower for sample with w/b ratio 0.3. The chemical shrinkage calculated from air voids and measured autogenous shrinkage can be well correlated to the hydration heat. [ABSTRACT FROM AUTHOR]

Corrosion of reinforcement and concrete deterioration induced by aggressive media could severely reduce the bearing capacity of structures. The durability of alkali-activated materials (AAMs) in aggressive environments, such as carbonation, chloride penetration and sulfate attack, have been a research focus worldwide. Reaction products and microstructures of AAMs are different from ordinary Portland cement (OPC), therefore the corrosion mechanisms and assessments are different. This paper reviews factors influencing water absorption and permeability of AAMs, effect of gel composition and exposure environments on carbonation, chloride penetration and chloride migration test methods, and sulfate resistance in high-calcium and low-calcium alkali-activated systems. There remains a large space in these aspects to completely understand the deterioration of AAMs, as pointed out in the end. The perspectives suggested in this paper will be useful for future study on long-term durability of AAMs. [ABSTRACT FROM AUTHOR]

Addition of limestone to Porland cement can significantly increase the hydration and high early strength of Porland cement. However its application in the magnesium phosphate cement is less known. In this paper, magnesium potassium phosphate cement (MKPC) pastes in which magnesium oxide was replaced by up to 30% limestone were studied. The effect of limestone content on the hydration temperature, setting time, compressive strength, and early water stability were investigated. The deterioration mechanism in water was explored by analyzing the pH value of the immersed solution, leached substances, total phosphorus content and microstructural analyses including X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TG/DTG) and mercury intrusion porosimetry (MIP). The results showed that addition of limestone into the magnesium phosphate cement matrix accelerated the setting time, decreased the total heat evolution of MKPC, and clearly degraded the strengths. The poor water stability of MKPC with limestone powder might be caused by the poor crystallinity and crystal morphologies of hydration products, worsened pore structure and increased dissolution of hydration products. Considering the materials costs and the strength development, the optimum addition of limestone powder should be no more than 10%. [ABSTRACT FROM AUTHOR]

High performance cement-based materials, such as high or ultra-high performance concrete (HPC or UHPC) have been widely used and still faces the risk of cracking caused by shrinkages, especially autogenous shrinkage. Internal curing is an effective method to reduce or even eliminate autogenous shrinkage and has effects on chemical shrinkage, dry shrinkage, etc. The commonly used internal curing materials include super-absorbent polymer (SAP) and porous materials. Porous materials refer to lightweight aggregate (LWA) and porous superfine powders. In this paper, the internal curing materials has been divided into two categories based on water absorbing mechanism. The effects of these two categories of internal curing materials on shrinkage of high performance cement-based materials are reviewed. The addition of internal curing materials releases internal curing water, postpones the drop of internal RH, and reduces autogenous shrinkage, but increase chemical shrinkage. The addition of internal curing materials with extra water increases drying shrinkage. The mechanisms of shrinkage on internal curing are also summarized and discussed. However, those mechanisms only focus on certain type of shrinkage. To reduce the risk of cracking more effectively, the relationship of different type of shrinkages should be established. [ABSTRACT FROM AUTHOR]

Alkali-silica reaction (ASR) is one of the durability factors limiting the commercial use of alkali-activated slag (AAS) concrete. The effect of alkali dosage is of great importance and barely studied for ASR in AAS system. This study investigates the effect of alkali dosage on ASR in sodium hydroxide (NaOH) activated slag mortars. In addition to ASR expansion, the changes in sample weight, compressive strength, pore structure, and pore solution chemistry are also investigated for better understanding the factors controlling the ASR in AAS mortars. The present study shows that the pore solution alkalinity increases with increasing the alkali dosage of the activator. However, the ASR expansion decreases with increasing the alkali dosage. The SEM/EDX results show no significant difference in both morphology and chemical composition of the ASR products. The lower ASR expansion at higher alkali dosage may be attributed to the relatively higher concentration of aluminum in the pore solution due to higher degree of slag hydration, which is expected to mitigate the dissolution of silica from the reactive aggregate. [ABSTRACT FROM AUTHOR]

This study investigated the effects of curing regimes (standard, hot water, and steam curing) on mechanical properties of ultra-high performance concrete (UHPC) with different supplementary cementitious materials (SCMs). The flowability, compressive strength, flexural load-deflection relationship, ultimate flexural strength, and toughness of UHPC mixtures with 0, 20%, 40%, and 60% of either ground granulated blast-furnace slag (GGBS) or fly ash, by the mass of cement, were evaluated. Test results indicated that the increase in GGBS or fly ash content had limited or negative influence on the compressive strength of UHPC in terms of curing regime type . For the flexural strength, there existed an optimal SCM content, which was 40% for GGBS and 20% for fly ash. Excessed this dosage could result in a drop in flexural strength and toughness. The hot water and steam curing significantly improved the flexural properties. However, prolonging the standard curing over 28 d led to comparable flexural properties as those under hot water and steam curing showed. The production of UHPC with appropriate GGBS or fly ash content with adequate standard curing, therefore, offers an effective way to obtain satisfactory flexural properties. [ABSTRACT FROM AUTHOR]

The effect of triisopropanol amine (TIPA), sodium chloride (NaCl) and limestone (LS) on compressive strength and hydration of Portland cement were studied using Design of Experiment (DoE) and isothermal calorimetry, respectively. The results showed that combination of TIPA and NaCl could increase both early age and later age compressive strength of Portland cement mortars and Portland cement–limestone mortars. No major interactive effects on strength enhancement were observed for these three additives. However, the results of isothermal calorimetry showed clear interaction between TIPA and NaCl. It was found that NaCl increased the effectiveness of TIPA through promotion of two transitions: (i) conversion of AFt to AFm for Portland cement sample, (ii) conversion of carboalumiante phases for Portland–limestone cement sample. [ABSTRACT FROM AUTHOR]

This study investigated the effects of three shaped steel fibers (straight, corrugated, and hooked-end) with different fiber contents by volume (V f = 0, 1%, 2%, and 3%) on mechanical properties of ultra high performance concrete (UHPC). The involved properties included flowability, compressive strength, and flexural behavior. According to the characteristics of the obtained three-point flexural load–deflection curve and the existing constitutive model of uniaxial compression, a new model for flexural load–deflection based on least square fitting was proposed. The results indicated that increased fiber content and use of deformed fibers could gradually decrease the flowability of UHPC. They also had significant effects on compressive and flexural behavior of UHPC. With incorporation of 3% straight steel fibers, its compressive and flexural strengths reached over 150 and 35 MPa at 28 d. For the concrete with 3% hooked-end and corrugated fibers, the compressive strengths at 28 d increased by 48% and 59% compared to those with the same amount of straight fiber. Steel fiber content had limited effect on the first crack strength and first crack deflection of flexural load–deflection curve of UHPC, but showed considerable effects on the peak load. The proposed model fitted well with the experimental results with correlation coefficient over 0.9. [ABSTRACT FROM AUTHOR]

Ultra high performance concrete (UHPC) refers to cement-based materials exhibiting compressive strength higher than 150 MPa, high ductility, and excellent durability. This paper reviews the theoretical principles, raw materials, mixture design methods, and preparation techniques for UHPC. Reduction in porosity, improvement in microstructure, enhancement in homogeneity, and increase in toughness are four basic principles for UHPC design. Raw materials, preparation technique, and curing regimes have significant influence on properties of UHPC. The use of widely available supplementary cementitious materials, such as fly ash and slag for partial/complete replacement of cement and silica fume, could significantly reduce the materials cost without sacrifice of strength. The use of high temperature curing results in denser microstructure and better performance than room temperature curing does, but obviously limits its applications of UHPC. Thus, preparation of UHPC using widely available raw materials, common technology, such as conventional casting and room temperature curing, are trends for production of UHPC. [ABSTRACT FROM AUTHOR]

This work investigated the effect of carbon dioxide treatment of recycled concrete aggregate (RCA) on the performance of RCA and RCA mortar. The results indicated that carbonation increased the apparent density, and reduced both water absorption and the crushing value of the RCA. The flowability and compressive strength of the RCA mortar were lower than those of natural sand mortar. However, the properties of mortar made with carbon dioxide treated RCA were very similar to those of natural sand mortar. Compared with the mortar made of un-carbonated RCA, the mortar made with carbonated RCA showed increased autogenous shrinkage, reduced drying shrinkage, water absorption, and chloride migration coefficient. Scanning electron microscope (SEM) examination on the interfacial transition zone (ITZ) in the RCA and RCA mortar found that carbonation treatment of RCA not only improved the original ITZ in the RCA, but also improved the newly formed ITZ in the RCA mortar. [ABSTRACT FROM AUTHOR]

Ultra high performance (UHPC) is a new cement based material, and it has aroused interest around the world since it was introduced in the early 1990s. Part I reviewed the theoretical principles, raw materials selection, mixture design and preparation techniques for UHPC. This part II reviewed the hydration, microstructure, mechanical properties, dimensional stability and durability of UHPC. Finally, some needs for future studies of UHPC are suggested. The portlandite of UHPC is much lower than that in the normal concrete. Heat curing could promote secondary hydration between mineral admixtures and Ca(OH) 2 , and xonolite was formed when the temperature was over 250 °C. UHPC has a very low porosity, especially under heat curing. UHPC has a character of high strength, stiffness and superior durability, etc. [ABSTRACT FROM AUTHOR]

Mixture design is a very important step in production and application of concrete. Many mixture design methods have been proposed for self-compacting concrete (SCC). This paper presents a critical review on SCC mixture design methods in publications. Based on principles, those methods can be classified into five categories including empirical design method, compressive strength method, close aggregate packing method and methods based on statistical factorial model and rheology of paste model. The procedures, advantages and disadvantages of each method were discussed. The most appropriate method should be chosen according to actual situations to obtain high quality SCC with satisfactory properties. [ABSTRACT FROM AUTHOR]

• Magneto-responsive rheology of highly flowable cement paste with PCE is studied. • Flowable cement paste with magnetic particles and PCE can exhibit MR response. • PCE increases relative MR effect while slightly decreases absolute MR effect. • Applying magnetic field plays a major role in stiffness for cement paste with PCE. Magneto-rheology control, by means of adding magnetizable particles and applying magnetic field, is a potential approach to satisfy the contradicting requirements of fresh properties in different casting processes. Polycarboxylate ether (PCE) superplasticizer is an essential component of modern cement-based materials, which significantly affects the viscoelastic properties of cementitious suspensions, and hence the movement and distribution of magnetic particles after applying an external magnetic field. This present research focuses on the following two aspects: whether highly flowable cementitious paste containing both magnetic particles and PCE shows rheological response to an external magnetic field, and if yes, is there a difference of magneto-responsive structural evolution of cementitious pastes with and without PCE? For these purposes, the magneto-responsive structural build-up of highly flowable cementitious pastes with various magnetic particles (two nano-Fe 3 O 4 particles and one magnetic fly ash) in the presence of PCE, described by the evolution of storage modulus over time, is evaluated. Experimental results show that highly flowable cementitious pastes containing both magnetic particles and PCE indeed exhibit obvious magneto-rheological (MR) responses. The incorporation of PCE significantly increases the relative MR effect while slightly decreases the absolute MR effect. By comparing the magneto-responsive structural build-up of cementitious pastes with and without PCE, it is revealed that the application of an external magnetic field to a highly flowable cementitious paste with PCE mainly plays a significant role in the increase of solid-like properties. [ABSTRACT FROM AUTHOR]

• The effects of slag/fly ash ratios, Na 2 O% and Ms of activators on the sulfate attack of AACs are studied. • Upon the Na 2 SO 4 attack, the C-A-S-H gel structures of AACs do not change basically. • The MgSO 4 attack on AACs is severe due to the dissolution of alkali and the migration of Mg2+. • Gypsum is the main product in AACs upon the MgSO 4 attack. • The effect of Ms on the sulfate resistance of AACs is related to the slag/fly ash ratios. In this work, the effects of slag/fly ash ratios, Na 2 O concentration, and silicate modulus (Ms) of activators on the reaction mechanism of sulfate attack on alkali-activated slag/fly ash cements are elucidated by XRD, FTIR, and TG/DTG analysis. To accelerate the sulfate attack process, the alkali-activated cements (AACs) were crushed into particle samples before immersion in the Na 2 SO 4 and MgSO 4 solutions. The results show that upon the Na 2 SO 4 attack, the C-A-S-H gel structures of AACs do not change basically. However, the MgSO 4 attack on AACs is severe due to the dissolution of alkali and the intrusion of Mg2+. Gypsum is the main product in AACs upon the MgSO 4 attack, and the amount of brucite decreases with the incorporation of fly ash. The NaOH-activated slag (Ms = 0) has a relatively higher MgSO 4 resistance compared with the Na 2 SiO 3 -activated slag, while it is the opposite when the fly ash replacement level increases to 80%. [ABSTRACT FROM AUTHOR]

Abstract: The effect of organic layered silicates (OLSs) on the flame retardancy and aging properties of the bitumen was investigated as well as the microstructures of the binders. X-ray diffraction shows that organic rectorite (OREC) and organic montmorillonite (OMMT) modified bitumens form the intercalated nanostructures, while the organic expanded vermiculite (OEVMT) modified bitumen forms the exfoliated nanostructure. The mass change rate and viscosity aging index of the bitumen are decreased by OLSs after thin film oven test and pressure aging vessel aging. Compared with OREC and OMMT, OEVMT has more pronounced improvements in flame retardancy and aging resistance of bitumen. [Copyright &y& Elsevier]

Abstract: It is a common practice to use steam to cure precast concrete products and concrete masonry blocks after casting. Steam curing is an energy extensive process and contributes significantly to the production costs. This study investigated the effects of pre-conditioning on the CO2 curing of lightweight concrete block mixtures. The results indicated that there was an optimum moisture loss at which the specimens demonstrated the highest strength and CO2 consumption after CO2 curing. However, the moisture evaporation rate had to be controlled so to avoid plastic shrinkage cracking. CO2 curing was an exothermal process, which raised the temperature of specimens very quickly within a short period of time. Traditional steam curing of concrete blocks took 18–24h, CO2 curing could be completed with 4–8h including pre-conditioning to achieve strength equivalent to that steam curing, This means that the use of CO2 curing technology has advantages not only in reducing and/or utilizing greenhouse gas emissions, but also in decreasing the curing time and increasing productivity of plain and non-steel reinforced concrete products. [Copyright &y& Elsevier]

Abstract: This paper reviews reaction mechanisms of AgNO3, AgNO3 +K2CrO4 and AgNO3 +fluoresceine colorimetric methods, and their applications for measurement of chloride ion penetration in concrete. Among the three methods, AgNO3 method is most widely applied because it gives similar results but simpler and faster than the other two methods. AgNO3-based colorimetric methods can potentially measure two variables, chloride ion penetration depth and chloride concentration at the color change boundary. Reported chloride ion concentrations at the color change boundary (C d ) measured or calculated by some researchers vary over a broad range due to many factors, such as sampling procedure, chloride ion analysis method, alkalinity of concrete, sprayed volume and concentration of AgNO3 solution, pore solution volume and methods for measuring free chloride concentration in concrete, etc., in which sprayed volume and concentration of AgNO3 solution are main factors. The smaller the volume of sprayed AgNO3 solution with a certain concentration, the lower the Cd is. 0.1mol/L AgNO3 solution has most clear color of boundary. To obtain a lower C d , a proper sprayed volume of 0.1mol/L AgNO3 solution should be determined. However, this important point was not mentioned at all times since the AgNO3 method was applied. Based on small range of Cd , AgNO3 method can be a useful method for rapidly evaluating chloride ion penetration in reinforced concrete structures in chloride environments. [Copyright &y& Elsevier]

Abstract: Elastic modulus is an important property of concrete and is used to calculate deformation of structures. Support vector machine (SVM) is firmly based on learning theory and uses regression technique by introducing accuracy insensitive loss function. This paper investigates the use of SVM to predict elastic modulus of normal and high strength concrete. The elastic modulus predicted by SVM was compared with the experimental data and those from other prediction models. SVM demonstrated good performance and proven to be better than other models. [Copyright &y& Elsevier]

Abstract: This paper reviews the chloride binding of cement-based materials subjected to external chloride environments. Chloride ion exist either in the pore solution, chemically bound to the hydration products, or physically held to the surface of the hydration products. Chloride binding of cement-based material is very complicated and influenced by many factors, such as chloride concentration, cement composition, hydroxyl concentration, cation of chloride salt, temperature, supplementary cementing materials, carbonation, sulfate ions and electrical field etc. Four different types of binding isotherms, namely linear, Langmuir, Freundlich and BET binding isotherm have been proposed to describe the relationship between free and bound chloride, none of which can accurately express the relationships between free and bound chloride within the whole concentration range. Freundlich binding isotherm seems to be the most approximate one. However, some field data fit linear isotherm well. This may be ascribed to the leakage of hydroxyl ion. Many service life prediction models based on diffusion mechanism alone have been proposed during the past two decades. If chloride ion binding is not considered in the models, it underestimates the predicated service life. [Copyright &y& Elsevier]

• Simplex design method was used to elucidate the composition-dependent mechanism. • Composition changes and properties were correlated via graphical visualization. • Relationships between the paste composition and its properties were developed. This paper aims to elucidate the effect of changes in the mix composition on the properties of Portland cement (PC)-metakaolin (MK)-limestone (LS) ternary system. To achieve this, the mixture proportion was optimized using the simplex design method and its effect on the properties of the binder was evaluated experimentally and correlated via graphical visualization. Experimental results confirmed the enhancement and acceleration of kinetics of cement hydration by LS and MK. However, a higher porosity was noticed at early age and was attributed to the high reactivity of MK which hindered it from acting as an effective filler. Therefore, the correlation between the optimum mix design and compressive strength was found to be dependent on the paste age. The findings of this paper would contribute to a better understanding of the dependence of the properties of PC-MK-LS ternary system on its composition. [ABSTRACT FROM AUTHOR]

• Changes in rheological properties of high-strength concrete due to pumping were systemically investigated. • Fresh concrete was sampled in dismantled pipes for the rheological test. • Shear-thickening in high-strength concrete was eliminated after pumping. • Shearing energy during agitation and pumping was estimated and correlated to the changes in viscosity. Pumping of high-strength concrete (HSC) in high-rise or long-span structures is of paramount importance in constructions. However, pumping technology in practice is highly dependent on practical field experience, and full-scale testing that is carried out for complex projects involving new materials or long pumping distances. In this paper, a long pumping circuit was built to study changes in fresh properties of HSC due to pumping. In total, 10 HSC mixtures with strength grades of C60 to C100 were pumped at constant flow rates in pipelines measuring 348, 600 and 924 m in length. Rheological properties, workability characteristics, and concrete temperature were measured on concrete specimens sampled before and after pumping. Rheological properties of concrete sampled in dismantled pipes shortly after the end of pumping were also determined. Test results indicated that the yield stress increased, the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated due to pumping. The increase in yield stress mostly occurred in the first half of the pipeline, and the tangential viscosity decreased nearly linearly along the pipe length. The levels of drop in initial tangential viscosity were found to positively correspond to the calculated shearing energy, which is estimated given the shear rate, apparent viscosity and elapsed time during agitation and pumping. [ABSTRACT FROM AUTHOR]

• Early CO 2 curing enhances the water infiltration and chloride permeability resistance of cement mortar. • Early CO 2 curing decreases the chloride binding capacity of cement paste. • The addition of fly ash reduces the chloride binding of early CO 2 cured cement paste. Early CO 2 curing has attracted a lot of attentions due to sequestration of carbon dioxide and rapid strength development for cement-based materials. This study investigates the chloride transport and binding properties of fly ash-blended cement-based materials with and without early CO 2 curing. A comparison is made between the specimens exposed to early CO 2 curing followed by subsequent water curing and those continuously cured in water. Results show that early CO 2 curing decreases the water sorption and chloride migration coefficient of cement mortar. The replacement of cement with fly ash decreases the strength and permeability of mortar regardless of the curing regime. CO 2 cured cement pastes show lower chloride binding capacity than water cured cement pastes after immersion in 0.1 M, 0.5 M and 1 M sodium chloride solutions due to the consumption of calcium hydroxide, presence of carbonates as well as lower contents of C-S-H gel. The presence of fly ash increases the contents of bound chloride in water cured cement pastes but decreases them in CO 2 cured cement pastes. [ABSTRACT FROM AUTHOR]

• This paper gives a comprehensive overview on accelerators for shotcrete. • The hydration mechanisms of Portland cement with accelerators are summarized clearly. • Durability of shotcrete are discussed and possible solutions are given. Accelerators are widely used in shotcrete to achieve rapid setting and hardening properties. This paper reviews different chemicals of accelerators and discusses their effects on hydration, microstructure and properties of cement-based materials. Generally, alkali aluminates, silicates, carbonates, etc. are main types of alkali used in alkali-containing accelerators while aluminum salts and alkanolamines are important components in alkali-free accelerators. These accelerators significantly promote the hydration of tricalcium silicate (C 3 S) and/or tricalcium aluminate (C 3 A), producing large amounts of calcium silicate hydrate (C-S-H) and/or calcium sulfoaluminates (AFt and AFm) at early hydration ages to shorten the setting times and increase early strength of cement-based materials. However, the accelerated formation of AFt and AFm, especially AFm, results in retardation of hydration of C 3 S. Most accelerators, especially alkali-containing accelerators, exhibit negative effects on long-term strength, shrinkage and durability of cement-based materials. The incorporation of reinforcement, supplementary cementitious materials, chemical admixtures etc. is a feasible approach to overcome these negative effects. This review also gives some perspectives for future development of accelerators for shotcrete. [ABSTRACT FROM AUTHOR]

• The effects of Na 2 O% and w/b ratio on the carbonation of AACs are studied. • In carbonated AAS, CaCO 3 increases when Na 2 O% increases from 4% to 8%. • In AACs with 60% slag, the decreased w/b ratio improves the carbonation resistance. • In AACs with 20% slag, the increased Na 2 O% reduces the carbonation degree. In this study, the effects of Na 2 O concentration and water/binder (w/b) ratio on the phase evolution and carbonation of alkali-activated slag/fly ash cements are studied. After sealed curing for 28 days, the alkali-activated cement powders were performed accelerated carbonation for 7, 14, 35, 60, and 120 days, at CO 2 concentrations of 1.0 ± 0.2%, 20 ± 2 °C, and RH = 65 ± 2%. In alkali-activated slag at w/b ratio = 0.5, when the Na 2 O concentration increases from 4% to 8%, the amount of calcium carbonates after carbonation increases due to a higher activation degree of slag and the decalcification of more C-A-S-H gels, but the crystallinity of calcium carbonates decreases. At a fixed Na 2 O concentration of 6%, when the w/b ratio decreases from 0.5 to 0.3, the formation rate of calcium carbonates and the crystallinity of calcium carbonates decrease. When the content of slag is 60%, the formation rate of calcium carbonates decreases with the increased Na 2 O concentration from 6% to 8%, due to the higher reaction degree of fly ash and the formation of more N-A-S-H gels; and the amount of calcium carbonates increases with the decreased w/b ratio. When the content of slag is 20%, the increased Na 2 O concentration could decrease the formation rate of calcium carbonates significantly, but the effect of the w/b ratio is limited. [ABSTRACT FROM AUTHOR]

• The factors affecting the effectiveness of internal curing was summarized. • The effects of characteristics of internal curing materials were systematically analyzed. • The in-situ water migration from the internal curing materials to the surroundings was discussed clearly. This paper mainly gives an overview of factors affecting the effectiveness of internal curing in cement-based materials from three aspects: the amount of internal curing water, characteristics of internal curing materials, and migration distance of internal curing water. It was found that (i) the equation developed to calculate the requirement of internal curing water for concretes with different water to cement ratios (w/c) based on Power's model that includes silica fume and to get a maximum degree of hydration by prewetted lightweight (LWA) could not completely reduce autogenous shrinkage, (ii) the water release characteristics of internal curing materials (e.g., the time to release and the distance to migrate) under uniformly distributed conditions may override the influence of the spacing factor, and (iii) unexpected effects resulting from internal curing on the properties of concrete may occur if the characteristics of internal curing materials do not match the pore structure of concrete mixture. [ABSTRACT FROM AUTHOR]

• As a nondestructive method, the EIS measurement is conducted for AAS and PC pastes. • Effects of alkali dosage on microstructure of AAS paste are studied. • An equivalent circuit model is proposed to analyze the microstructure development. • The pore structure and pore solution chemistry are investigated. In this study, electrical impedance spectroscopy (EIS) is applied to investigate the effect of alkali dosage on the microstructural evolution of the alkali-activated slag (AAS) system during the curing process. Pore solution chemistry and pore structure of the paste samples were also determined to get auxiliary interpretation of the EIS results. It is shown by equivalent circuit analysis that the resistance attributed to continuous (R 1) and discontinuous pores (R 2) increases with curing age due to pore structure development. The value of R 1 is more affected by pore solution chemistry while the value of R 2 is mainly affected by pore structure. With the increase of alkali dosage, the value of R 1 decreases while R 2 gradually increases. The exponent n of the constant phase element (CPE), which relates to the capillary pores (n 1), decreases with the increase of alkali dosage while the exponent relating to gel pores (n 2) is independent of the alkali dosage of AAS paste. The bulk conductivity of AAS paste obtained from the bulk resistance gradually increases with the alkali dosage, partially because of the enhanced conductivity of pore solution. The improvement of microstructure at early age is mainly attributed to the decreased porosity, which is more affected by the pore connectivity with the increase of curing age. These results confirm that EIS is an effective technique to determine the hydration properties and pore structure features of AAS paste. [ABSTRACT FROM AUTHOR]

• The interactions between PCE and clay minerals before and after calcination are discussed clearly. • The enhancement techniques for the tolerance of PCEs to clays are outlined. • The effects of use of sacrificial agents and molecular design on clays-resistance of PCEs are analyzed. Polycarboxylate ether/ester (PCE) superplasticizers are widely used due to their molecular structural designability, low dosage and high efficiency. However, their high sensitivity and strong interactions with clays in concrete reduce their dispersion and water-reduction capability, which can affect the performance of concrete seriously. This paper reviews the interactions between PCE superplasticizers and clays before and after calcination, and the enhancement techniques of the resistance of PCE superplasticizers to clays, and points out their advantages and disadvantages. Reduction in the number of active sites of clays by the addition of small molecular polymers as sacrificial agents can decrease the physical and chemical adsorption of PCEs. Introduction of functional groups into PCE can restrain its intercalation by clays. Apparently, more clays robust PCE superplasticizers can be achieved via molecular design. This review can provide a direction for the further design and development of PCE superplasticizers. [ABSTRACT FROM AUTHOR]

• Analytical solution to Couette inverse problem of Herschel-Bulkley fluid was derived. • The transformation equation was validated by both computer synthesized and experimental data. • Comparison between the analytical equation and the approximation equation was conducted. The Herschel-Bulkley model is one of the most commonly used rheological models for Non-Newtonian fluids, and it has been applied to describe the non-linear rheological behavior of fresh concrete. However, because it is difficult to transform the measured rotating speed and torque data into fundamental rheological units for coaxial cylinder rheometers, only an approximate approach has been proposed for this model. In order to improve the accuracy of the solution, a new integral equation describing the torque-rotation speed of Herschel-Bulkley model was derived in this paper, and 40 sets of simulated data were used for the comparison between the two methods. The equation introduced in this study was further validated by the experimental data of SCC. The results indicated that the established solution yielded more accurate results than the approximate one. [ABSTRACT FROM AUTHOR]

• The microstructure and interfacial properties of cement paste are studied. • The modifications of electrical parameters due to chloride penetration are studied. • The properties of EDL are discussed by the obtained capacitance. • The calculated EDL thickness is correlated to the chloride concentration in EDL. In this paper, the characteristics of AC impedance spectroscopy of cement paste immersed in chloride solution were measured and analyzed with a proposed equivalent circuit model. The elements in the proposed equivalent circuit, including the resistance of interface between electrode and specimens, resistance of continuous and discontinuous pore, capacitance of solid phase and electrical double layer (EDL) were discussed. The results showed that the resistance of interface between electrode and testing specimen was much lower than that of cement paste. With the increase of chloride concentration in the soaking solution, the resistance of continuous gradually decreased due to the higher conductivity of chloride solution. Stripped out the impacts of concentration of pore solution on resistance of pores, the resistance of continuous pore increased firstly due to the decrease of continuous pore volume from the formation of Friedel's salt. However, the resistance of discontinuous pores gradually decreased with the increase of soaking solution concentration due to the transformation of continuous pores to discontinuous pores. The reaction between chloride ions and hydration products and formation of Friedel's salt decreased the porosity of cement pastes and led to higher capacitance of solid phase. Based on an idealized two-plate capacitor model for EDL, the thickness of EDL was calculated from the measured capacitance. The decrease of EDL thickness with chloride concentration in soaking solution was in agreement with the results of chloride contents in EDL obtained from pore solution expression test. [ABSTRACT FROM AUTHOR]

• Effects of different factors on chloride concentration index (N c) of cement paste are studied. • Zeta potential, thickness and chloride distribution of EDL are investigated. • The relationship between N c and properties of EDL are modeled and studied. In this study, the effects of different factors on chloride concentration index (N c) of cement paste were studied. The factors including chloride concentration in soaking solution, slag replacement, external applied voltage and cation ions of soaking solution were all studied from the electrical double layer (EDL) properties point of view. Zeta potential and proton Nuclear Magnetic Resonance (1H NMR) measurements were conducted to investigate the properties of electrical double layer for cement paste specimens and their effects on the value of chloride concentration index. The results showed that these factors all impacted effects on chloride concentration in electrical double layer and chloride concentration index. The properties of electrical double layer including chloride distribution and thickness of electrical double layer mainly controlled the phenomenon of "chloride concentrate" and value of chloride concentration index. As the increase of zeta potential and electrical double layer thickness, the content of chloride ions in electrical double layer and the value of chloride concentration index gradually increased. [ABSTRACT FROM AUTHOR]

• Water desorption was summarized and discussed from three factors: time and amount and migration distance of water released. • Characterization of ITZ between cement paste matrix and LWA was summarized. • What's important is that pore structure of LWA matches that of concrete. • The saturation of capillary pore should be related with internal RH. Lightweight aggregate (LWA) has been used in concrete for a long time, but its internal curing (IC) effect has been realized recently. This paper offers a review of LWA as internal curing materials for high performance cement-based materials. The effect of LWA on IC is related to its amount, pretreatment method, particle size, and distribution in concrete. Pre-wetted LWA has a better IC effect than dry LWA. The particle size of LWA and its distribution in concrete are two important factors to achieve satisfactory IC effectiveness such as concrete strength and autogenous shrinkage, which need to be further studied. The effects of LWA on the strength depends on two opposite facts: the side effect of LWA's porous structure and beneficial effect of internal curing on the hydration. The desorption of IC water is related to the size ranges of pores in LWA and paste, and large pore sizes of current LWA cause a quick desorption of IC water in concrete with low water-to-binder ratio. Water release of LWA promotes the hydration and refines the pore structure. Interfacial transition zone (ITZ) between cement paste matrix and LWA is also improved and the permeability is reduced. The characterization of ITZ surrounding LWA is a key point to understand the IC mechanism and a feasible method needs to be put forward. Those studies will provide a better theoretical foundation for the preparation of high performance LWA cement-based materials. [ABSTRACT FROM AUTHOR]

• The SAPs located at the vicinity of the exposed surface lowered the evaporation of water. • Lower contribution of evaporation on IRH drop at inner layers magnified the effect of SAP on controlling the shrinkage. • The drying environment had less influence on the performance of SAP in larger UHSC specimens. In this study, effects of super-absorbent polymer (SAP) on shrinkage of ultra-high strength concrete (UHSC) under drying condition were investigated. The total shrinkage and autogenous shrinkage of UHSC specimens of two sizes with and without SAP were measured and the associated drying shrinkage was calculated. In addition, the internal relative humidity (IRH), free water and chemically bound water at different distances from the drying surface were obtained and compared to the sealed specimens in order to analyze the shrinkage mechanism of UHSC with SAP under drying condition. The results showed that SAP caused uneven moisture distribution at the inner and outer layers based on the distance from the drying surface. The release of water from SAP was faster at distances within 3 cm from the drying surface, and the IRH dropped more rapidly comparing to inner layers. At layers within 3–10 cm from the drying surface, SAP was able to maintain the IRH comparable to those under sealed condition. Accordingly, the drying environment had less influence on the performance of SAP in larger UHSC specimens, and restraining effect of SAP on shrinkage was superior to that of small ones. In addition, the moisture gradient at inner and outer layers led to different amounts of free water and chemically bound water throughout the matrix. The total shrinkage of UHSC under drying condition had a non-linear relationship with the average moisture loss due to the coupled effect of self-desiccation and migration of water to the surface due to evaporation. [ABSTRACT FROM AUTHOR]

Very low water-to-binder ratio of ultra-high performance concrete (UHPC) may facilitate using seawater as the mixing water, as there may not be sufficient moisture and air in its dense matrix to initiate the corrosion of steel reinforcements. However, extensive research is needed to investigate the effects of intermixed chloride from seawater on fresh and hardened properties UHPC. This study investigated the role of seawater in the interaction of slag and silica fume with cement in very low water-to-binder paste of UHPC at early ages of hydration. The results showed that seawater increased the reactivity of slag and enhanced its interaction with cement due to triggered reactions between seawater components and rich Al-phases in cement and slag. On the contrary, seawater decreased the interaction of silica fume with cement. The overall influence of seawater in the low water-to-binder paste enhanced the hydration kinetics of binary and ternary binders and restrained the autogenous shrinkage. Furthermore, the early age compressive strength was increased. The findings of the study showed that using seawater was in favor of early age properties of paste with very low water-to-binder ratio. [ABSTRACT FROM AUTHOR]

In this study, chloride ion concentration in the water extracted solution was measured. For comparison, it was also calculated based on the electrical double layer model under extraction equilibrium. The results indicated that the release of physically bound chloride can result in 1–7 times higher water extracted chloride ion concentration than free chloride ion concentration. With increase of fineness of powder, the chloride ion concentration in the water extracted solution increased. When powder fineness was higher than 1 µm, a very small amount of water could completely extract the water soluble chloride under extraction equilibrium. With increase of water/solid ratio and water temperature, release of chemically bound chloride led to a higher concentration of chloride ions in water extracted solution. The calculation is very helpful for discussing the effects of physically and chemically bound chlorides on extraction of water soluble chloride. Finally, suggestions for improvement of water extraction method were proposed by taking into account the experimental parameters influencing the release of bound chloride. [ABSTRACT FROM AUTHOR]

In this paper, the effects of curing conditions (dry air, moist air and water), state of water (static water and flowing water) and initial air curing time (5 h, 3 d and 28 d) on the corrosion behavior of magnesium–potassium phosphate cement (MKPC) paste subjected to water attack were investigated. The strength residual ratio and mass loss rate were used as deterioration indexes of MKPC paste in water. The pH value and leaching amounts of soaking liquid were also employed to evaluate the water corrosion behavior. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetry analysis (TG) and mercury intrusion porosimetry (MIP) were used to investigate the microstructure of MKPC paste before and after water corrosion. The experimental results showed that the water environment lead to a lower compressive strength of MKPC pastes, but the strength loss of MKPC paste under the flowing water curing was higher. Furthermore, prolonged initial air curing time could improve the water resistance of MKPC pastes, the specimens cured in air for the first 3 days then in water showed the best water resistance among all specimens immersed in water for 60 days. The deterioration mechanism of MKPC paste derived from the strength and mass loss test results was also clarified based on microstructural observation. [ABSTRACT FROM AUTHOR]