CEMENT最新文献

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.

This paper examines the sustainability of cementitious materials and concrete. Although the environmental impact of these materials is often evaluated based on their CO₂ emissions per ton of cement or m³ of concrete, incorporating performance parameters into sustainability indices is crucial for a more comprehensive assessment. This study evaluates the sustainability of concretes with and without supplementary cementitious materials (SCM), considering compressive strength and durability performance as performance parameters. Results show that the most sustainable concretes have the highest compressive strength and best durability performance. Furthermore, the importance of using locally available materials is highlighted, as transporting SCM over long distances can outweigh the benefits of using them as a replacement for Portland cement.

This paper presents a study investigating for the first time the effects of the inclusion of graphene nanoplatelets (GNPs) on the mechanical and microstructural properties of alkali activated binders produced with fly ash and slag and using superplasticizer for the GNPs dispersion in the mixing water. Compressive strength and water absorption of mortar cubes, flexural strength of mortar beams, X-ray computer tomography scanning and mercury intrusion porosimetry, Fourier transform infrared spectroscopy, scanning electron microscopy with Energy Dispersive X-Ray Spectroscopy, and X-ray diffraction, were carried out on samples cured either at room temperature or at 40 °C. Results showed that the inclusion of GNPs at a dosage of 0.05% provided a considerable increase in compressive strength at both curing conditions. Microstructural observations suggested that the presence of GNPs improved the formation of hydrated gel, and the research demonstrated through porosity measurements the shift from the capillary to the gel pore region due to the inclusion of GNPs. This study represents a step forward in understanding the effects of GNPs inclusion on alkali activated binder microstructure.