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Mixtures of powders of waste glass (WG), limestone (LS), Na 2 CO 3 and CaO were used to formulate novel one-part in situ alkali-activated cement (WG-AAC). The in-situ interaction Na 2 CO 3 -CaO-H 2 O promoted the formation of CaCO 3 and NaOH, which promoted the WG and LS dissolution and influenced the micro- and molecular features of the resulting cementitious products. Pastes and mortars developed 1-year strengths of up to 29 MPa and were stable underwater. Characterization by XRD, SEM, EDS, and 29 Si -NMR indicated that a Na 2 CO 3 :CaO ratio close to 1:1 resulted in polymerized C-S-H, CaCO 3 , silica gel, and Ca-modified silica gel, which were intimately intermixed and possibly crosslinked through Q3 bonds. Such phases interacted synergistically improving the underwater stability of the WG-AAC, indicating that in-situ caustification is a suitable and practical alkaline activation for SiO 2 -rich precursors. • One-part activation of waste glass produced mortars with up to 29 MPa and stable underwater. • Caustification reactions positively influenced the micro and molecular features of the matrix. • Ca-modified silica gel, CaCO 3 , C-S-H and silica gel coexisted synergistically. [ABSTRACT FROM AUTHOR]

Biomass ash results from the combustion of agricultural residues, which, in many developing countries, are a primary source of power generation for small and medium size industries. This study focuses on the performance of a binder synthesized from an Indian biomass ash, Indo-Gangetic clay, hydrated lime, and aqueous 1M NaOH solution. To measure the extent of leaching and its impact on physicochemical properties, the biomass ash binder in powder form (<45 μm size) was exposed to two different leaching media: deionized water and 0.1M HNO 3 at two different solution-to-sample ratios (by wt.) of 10 and 100. Sodium leaching was found to be prominent in the biomass ash binder irrespective of leaching medium and solution-to-sample ratio. However, calcium leaching was significantly higher in 0.1M HNO 3 than in deionized water. Calcium silicate hydrate present in the biomass ash binder was found to be less chemically stable in 0.1M HNO 3 , exhibiting complete calcium leaching at a solution-to-sample ratio of 100. Furthermore, significant leaching of calcium in 0.1M HNO 3 solution resulted in phase modification of calcium silicate hydrate, the main reaction product of the biomass ash binder. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cements exhibit useful properties such as shrinkage compensation and rapid strength development. Acid resistance of CSA cement is majorly governed by its phase composition that varies significantly depending on the desired properties. In this study, acid resistance of CSA cement (i.e., non-expansive) and gypsum blended CSA cement (i.e., expansive) is explored. The current work emphasizes that a small change in phase assemblage can cause large difference in the performance under acidic environment. Conventional acid immersion tests with hydrochloric acid (HCl) of 1 % and 2 % conc., and sulfuric acid (H 2 SO 4) of 2.95 % conc. were considered in the study. Furthermore, a recently developed acid consumption method was used to rank the binders with regard to their acid resistance in HCl and H 2 SO 4 environments. It was found that the gypsum-blended CSA cement showed poorer performance than CSA cement in acidic environment despite having marginally higher compressive strength before the acid exposure. [ABSTRACT FROM AUTHOR]

Biogenic acid attack of concrete is prevalent in sewers, posing a serious durability concern and financial burden. There are very limited number of field studies on durability of concrete under biogenic acid attack. Field study poses challenges with respect to the variation in climatic conditions and limited accessibility in sewers. Such a biogenic acid attack study in Indian conditions has not been performed. In this study, the biogenic acid resistance of Portland cement (PC) and calcium sulfoaluminate (CSA) cement-based binders under an in-situ sewer exposure is reported. The results show that the CSA-based binder used in this study outperformed PC in the biogenic acid resistance. The superior performance of CSA-based binder could be attributed to its acid neutralisation capacity offered by the aluminum hydroxide phase and bactericidal properties. For the first time, the bacteriostatic effect of CSA cement was demonstrated by analyzing the field exposed specimens. [Display omitted] [ABSTRACT FROM AUTHOR]

While the incineration of biomass residues is gaining traction as a globally available source of renewable energy, the resulting ash is often landfilled, resulting in the disposal of what could otherwise be used in value-added products. This research focuses on the beneficial use of predominantly rice husk and sugarcane bagasse-based mixed biomass ashes, obtained from two paper mills in northern India. A cementitious binder was formulated from biomass ash, clay, and hydrated lime (70:20:10 by mass, respectively) using 2M NaOH solution at a liquid-to-solid mass ratio of 0.40. Compressive strength of the biomass ash binder increased linearly with compaction pressure, indicating the role of packing density. Between the two mixed biomass ashes used in this study, the one with higher amorphous content resulted in a binder with higher strength and denser reaction product. Multi-faceted characterization of the biomass ash binder indicated the presence of aluminum-substituted calcium silicate hydrate, mainly derived from the pozzolanic reaction. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cement-based binders are low CO 2 binders which exhibit rapid hardening or shrinkage compensating characteristics. Due to their unique properties, they have potential to be used in concrete elements exposed to acidic environment such as sewage system. In this paper, the performance of CSA-based binders in acidic environment is examined and compared against Portland cement (PC). Attack of sulfuric acid and citric acid on PC and CSA-based binders was evaluated with respect to mass loss, dimensional change, cumulative H+ ion neutralisation, strength loss, and changes in mineralogical and microstructural characteristics. CSA-based binder exhibited higher resistance than PC-dominated binder in citric acid attack (pH ∼ 2–3), whereas PC-dominated binder outperformed CSA-based binder in case of sulfuric acid attack (pH ∼ 1.5–2). The mechanism of acid attack was found to be dependent on acid type. A calcium citrate salt was identified as the major product in case of citric acid attack of PC-dominated binders. [ABSTRACT FROM AUTHOR]

Expansive characteristics of calcium sulfoaluminate-belite (CSAB) cement can be harnessed for making shrinkage-compensating concrete. The level of expansion is dependent on several factors, such as the amounts of ye'elimite and calcium sulfate available in CSAB cement. Moreover, calcium sulfate from an external source can also influence the expansion characteristics by increasing the supersaturation with respect to ettringite. In this study, the influence of externally available calcium sulfate was investigated by curing a blend of Portland cement (PC) and CSAB cement to different concentrations (1 g/l and 5 g/l) of gypsum solutions. Expansion of the PC-CSAB blended cement was found to be directly affected by the ye'elimite content (CSAB dosage) and the gypsum concentration in exposure solution. The presence of external calcium sulfate during the hydration of ye'elimite was found to affect the hydrate phase assemblage, the pore structure, and the morphology of ettringite. Furthermore, the level of expansion depended on the age at which the specimens were exposed to the gypsum solution, indicating the influence of matrix stiffness on resultant expansion. [ABSTRACT FROM AUTHOR]