CEMENT最新文献

The attractive properties of ye'elimite (C₄A₃$) are receiving particular attention in cement and repairing materials. The present paper aims to further explore the difference in hydration performance of different C₄A₃$ phases (o-C₄A₃$ and c-C₄A₃$) using the Ga-doping method. On this basis, C₄A_3-xG_x$ specimens (noted as C₄A₃$, C₄A_2.3G_0.7$, and C₄A_1.6G_1.4$) were first synthesized and their hydration characteristics were systematically studied. Results showed that Ga-doping enhanced the hydration activity of ye'elimite. With increasing Ga³⁺ ions addition, the intensity of the initial peak gradually increased, but the duration of the induction period and the hydration heat development rate were gradually reduced. The conductivity and pore solution analysis also demonstrated a higher ion concentration precipitation at the early stage for cubic C₄A_1.6G_1.4$ compared to pure C₄A₃$. The main hydration products of these specimens were AFt, AFm, and AH₃ (gel). Moreover, the addition of Ga³⁺ ions improved the crystallinity of AFt and AFm with recorded a relatively higher decomposition temperature. Overall, this study demonstrated that the addition of Ga³⁺ ions can regulate the hydration characteristics of ye'elimite.

Corrosion of steel strand embedded in deficient grout has been associated with elevated concentrations of sulfate ions stemming from grout segregation and the adverse influences of excess mix water and grout prehydration. There have been discussions about appropriate ways to assess sulfate ion levels in the grout pore water. Various test methodologies can include varying material conditioning procedures, including heating, drying, and chemical reactions that can influence the level of sulfate ion aggregation in the test leachate from the initial bleed water from the bulk material. In this study, the sulfate content was measured by leaching and alternative methods such as XRF and bleed water testing. Six leaching methods were employed to assess the effect of leaching heating, heating time, leaching volume, grout sample mass, and drying temperature. Leaching of larger grout sample mass can yield higher leachate sulfate concentrations, but the concentrations were not commensurate with the larger grout mass. Leaching of a larger grout sample mass with a mass-to-water ratio of 1:10 was not shown to be efficient in the dissolution of sulfate ions. Larger mass-to-water ratio (1:40) yielded higher sulfate concentrations in the leachate and normalized grout mass. Pre-drying of grout samples to 100 °C for 24 h was shown to incur losses in sulfate content. Recommendations of test methods to assess the sulfate ion content from segregated and hardened grout were made.

The production of concrete has gone up from 2.3 billion m³ in 2002 to 14 billion m³ in 2020. At the same time, the amount of construction and demolition waste generated annually has reached levels of 3 billion tons, with concrete rubble making up a major portion of it. This study investigates the performance of carbonated fines derived from hydrated cement paste of different binders. Four cement paste blends, containing Portland cement (PC) and blends of Portland cement with fly ash (FA30), perlite (PL30) and metakaolin (MK30) at a 30 % cement replacement level, were cured for 90 days prior to subjecting them to a carbonation reaction. The R³ test gauged pozzolanic reactivity, while calorimetry, XRD, and TGA studied hydration characteristics. Compressive strength of mortar samples prepared using the same binder composition as paste was also measured at different ages. Carbonated fines exhibited notable pozzolanic activity compared to waste hydrated cement paste. The reactivity of carbonated fines derived from different binders were similar, however slightly higher reactivity was measured for fines comprising of reactive SCM in the precursor material (hydrated paste). Mixes with carbonated fines demonstrated enhanced kinetics, exhibiting over 25 % higher compressive strength at 3 and 7 days compared to the fly ash control mix. Similar compressive strength characteristics were observed in mortar mixes with different carbonated fines, indicating a limited impact of the various binder types from which the fines originated.

This article presents an investigation into the potential use of ground granulated blast-furnace slag (addressed as Slag cement or ‘SC’) as a replacement to Ordinary Portland Cement (OPC) in hybrid (carbonation and hydration) cured cement-based materials. To investigate the effects of carbonation on mechanical performances and microstructures, 0 %–100 % OPC was replaced with slag cement (SC). Thermogravimetric analysis (TGA) and Fourier transformed infrared (FTIR) spectra were utilized to investigate the carbonation reaction extent, rate, and microstructural phase formations. Slag cement was found to improve the efficiency and rate of carbonation. This study revealed that a minimum of 72 h of carbonation in a CO₂-containing environment yields better mechanical performance compared to the traditional curing method. Specifically, the incorporation of 72 h of carbonation curing was observed to increase the strength of concrete up to 30 % after 28 days of total curing duration (carbonation and hydration). The chloride permeability of the carbonation cured samples was observed to reduce by 80 % due to the addition of SC. Finally, it was observed that, the carbonated concrete sample with slag has nearly 60 % lower global warming potential compared to the carbonated and non-carbonated concrete sample with 100 % OPC binder.

This study examines the regional variability in the chemical composition and pozzolanic reactivity of corn stover ash (CSA) produced from corn stover samples collected from different locations in the U.S. Corn stover samples were collected from local farms in Nebraska and Iowa, while information about Kansas CSA was obtained from existing literature. The findings reveal significant variability in the chemical composition of untreated CSA across different regions. However, through the use of pretreatment techniques such as acid soaking, the compositional variations can be considerably reduced. The results of the modified R³ test demonstrate that CSA exhibits pozzolanic behavior that falls between that of fly ash and silica fume. The reactivity of CSA was found to be independent of geospatial factors but heavily influenced by the specific pretreatment methods employed in the study. Furthermore, the study indicates that the reactivity of CSA is less variable compared to fly ash and silica fume.

Ground granulated blast furnace slag (GGBS) is an important supplementary cementitious material (SCM) for producing low carbon and durable concrete. There are however questions around the early age reactivity of GGBS and the factors that influence this. To elucidate the fundamental mechanisms controlling the early age reactivity and particularly the influence of anionic species, simplified systems comprising GGBS and calcium hydroxide were examined in the presence of limestone, anhydrite, or both at 4:1 SCM-to-activator ratio. Limestone and GGBS were considered as SCMs, but calcium hydroxide and anhydrite were considered as activators. Multiple techniques, including isothermal calorimetry, thermogravimetry, X-ray diffraction, electron microscopy, mass balance calculation and mercury intrusion porosimetry were used to study hydration and microstructure. The results show that GGBS hydration commences immediately in the alkaline media provided by calcium hydroxide. Sulphates and limestone influence hydration through reactions with aluminates to form ettringite and carboaluminates, but prevalence of macro-capillary pores in sulphate containing binders sustains diffusion-controlled hydration. Consequently, optimization of the alumina to sulphate and carbonate ratios is essential for exploiting the pore solution and space filling effects in composite cements.

This study investigates the resistance against alkali-silica reaction (ASR) of two alternative binder systems, alkali-activated slag (AAS) and Celitement (Celite). Experimental studies on expansion and mechanical strength are carried out. Coupled kinetic and equilibrium thermodynamic modeling is used to clarify the role of binder chemistry on ASR. It was observed that under accelerated conditions OPC based mortars were more susceptible to ASR compared to AAS and Celite-based mortars. Based on experimental and modeling results, a correlation is shown between the dissolution of silica and the degree of expansion, but no correlation was found between the predicted amount of ASR products and the measured degree of expansion. Finally, the expansion degree could only be correlated with the reduction in compressive and flexural tensile strength for ASR-exposed samples.

In this work, Cold Water Extraction (CWE) was performed on blended cement pastes to extract the pore solution and determine the free alkali metal content. To better understand CWE results, the reactivity of cementitious materials was also investigated, complemented by TGA and quantitative XRD analysis. The study aimed at being generic to assess the suitability of the methods, and included 9 SCMs with various compositions: limestone, coal fly ash, two calcined clays, two biomass ashes, sewage sludge ash, crushed brick and glass beads.

The study highlighted the importance of assessing the reactivity of SCMs in parallel to performing CWE, as this contributes to a more certain interpretation of the results. In general, results obtained with CWE were consistent with the existing literature about the effect of binder composition on the free alkali metal content. From a practical view, CWE and SCM reactivity tests could be performed with basic laboratory equipment and appeared to be applicable to both traditional and alternative SCMs.

The concrete industry faces an urgent need to identify new supplementary cementitious material (SCM) sources. One class of materials available in large volumes are basaltic materials, which are often stockpiled in landfills as a waste product from quarries and granule operations. Reactivity testing on some such materials has shown them to be inert. The thermal activation of basaltic fines, and their mixtures with fly ash and limestone was therefore evaluated in a furnace using different process variables. Physical and chemical characterization using X-ray diffraction, Fourier transform infrared spectroscopy, and electron microscopy was performed on the raw and thermally activated materials. The reactivity of the resulting materials was directly measured. Heating beyond 1300 °C and cooling results in complete amorphization for the tested materials and resulted in the highest reactivity. Thus, the activation of basaltic fines into SCMs is feasible, although optimization to reduce temperatures is needed.