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The high-belite calcium sulfoaluminate cement (HB-CSA) has displayed outstanding acid resistance. However, further research is needed to understand the mechanism behind its acid resistance fully. This study investigates the resistance of a new type of HB-CSA to hydrochloric and sulfuric acid. Additionally, the impact of the ye'elimite (C4A3S)-to-gypsum (CS) ratio on the acid resistance of HB-CSA is discussed. The resistance performance is investigated by flexural strength and resistance index analyses, X-ray diffraction (XRD), thermogravimetric analysis (TGA), electronic computed tomography (CT) scans, and scanning electron microscopy (SEM). The results show that the HBCSA exhibits superior resistance to sulfuric acid and hydrochloric acid compared to Portland cement. The absence of portlandite contributes to the enhanced performance of HB-CSA. In addition, as the C4A3S-to-CS ratio decreases, the content of Aft in HB-CSA increases, leading to an increase in the acid resistance of HB-CSA. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace slag is considered a potential material for the replacement of natural aggregate in Portland cement concrete due to its similar physical characteristics. Therefore, in the present work, the slag was analyzed by Nitrogen sorption porosimetry, elemental analysis, mineralogical analysis, and volume stability. On the other hand, concrete mixtures were manufactured with basic oxygen furnace (BOF) slag aggregates and characterized mechanically and morphologically. The results showed superior compressive strength due to interfacial improvements in the slag aggregate. Statistically, there was no differentiation between the reference concrete and the slag concrete mixtures for tensile strength. Additionally, due to the porosity and low stiffness presented by the slag, the concrete elastic modulus showed a slight decrease. The replacement of sand with BOF slag as fine aggregate in Portland cement concrete presents itself as a sustainable alternative for the elimination and valorization of this environmental liability. [ABSTRACT FROM AUTHOR]

Acidic environments constitute serious chemical threats to concrete-like cementitious materials. The purpose of this study is to experimentally investigate the degradation of alkali-activated slag/fly ash mortars with different slag/fly ash ratios: 80/20 , 60/40 , and 40/60 in acidic environments. Mortar samples were exposed to three different types of aggressive acidic solutions: phosphoric acid, sulfuric acid, and a mixture of phosphoric acid and sulfuric acid maintained at a constant pH value of 2.5±0.5 for a period of 150 days. Results showed that, for all mortar samples, the aggressivity of the phosphoric acid is greater compared to the other acids. Moreover, samples with a slag/fly ash ratio of 60/40 demonstrate the highest resistance against the three types of acidic environments. In addition, it shows that the degradation process of alkali-activated mortars can be divided into two degradation stages: an early stage and a subsequent stage. The chemical-reaction dominated early degradation stage is described by using Hill function, whereas a diffusion process–dominated subsequent stage is simulated with Fick's second law. Finally, the results of theoretical analysis predicted that the degradation depth of alkali-activated slag/fly ash mortars exposed to sulfuric acid environment (pH=2.0) for 50 years could be reduced by about 52%–60% compared to that of an ordinary Portland cement (OPC)-based mortar. [ABSTRACT FROM AUTHOR]

In this paper, we comparitvley studied acetic acid attacks on geopolymer (GP-M), calcium aluminate (CAC-M), and Portland cement (PC-M)-based mortars. Consequent formations of deteriorated or transition layers surrounding the unaltered core material was classified in these three mortars, according to different degradation levels depending on what binder type was involved. Apart from mass loss, hardness, and deterioration depth, their microstructural alterations were analyzed using test methods such as scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), mercury intrusion porosimetry (MIP), powder X-ray diffraction (XRD), and thermogravimetric analysis-differential scanning calorimeter (TGA-DSC), which showed the different mechanisms for each binder type. Elemental maps revealed the decalcification (PC-M and CAC-M) and depolymerization (GP-M) that occurred across the mortar sections. The mass loss, hardness, and porosity were the least affected for GP-M, followed by CAC-M. These results points out that geopolymer-based mortars have improved acid resistance, which can be used as a potential alternative to conventional cement concretes that have been exposed to agro-industrial environments. [ABSTRACT FROM AUTHOR]

This study investigated the reactivity properties of self-leveling hybrid alkali-activated cements, such as ordinary Portland cement (OPC) and its residual precursors, coal bottom ash (BA), and rice husk ash (RHA). Due to the relatively low reactivity of BA, binary mixes were produced with OPC using contents of 2.5–30% in the treated BA samples. Furthermore, ternary mixes were prepared in proportions of 25%, 50%, and 75% with RHA as a replacement material for the OPC (mix with 90%:10% BA:OPC). For all of the mixes the spreading behaviors were fixed to obtain a self-levelling mortar, and dimensional changes, such as curling and shrinkage, were performed. Mortars with 30% OPC reached a compressive strength of 33.5 MPa and flexural strength of 7.53 MPa. A scanning electron microscope (SEM) and X-ray powder diffraction (XRD) were used to indicate the formation of N-A-S-H and a (N,C)-A-S-H gel, similar to the gel with trace of calcium. The best performance was achieved when the binary mix produced 10% OPC. A hybrid mortar of OPS-BA presented 10 times lower susceptibility to curling than an OPC mortar. The results showed that both ashes reduced the shrinkage and curling phenomena. [ABSTRACT FROM AUTHOR]