Characterization of washing aggregate sludge waste as a novel supplementary cementitious material: Experimental study and life cycle assessment.

Washing aggregate sludge (WAS), a waste collected from aggregate quarries, is examined for its application as a partial substitute of ordinary portland cement (OPC). The raw WAS initially dried, ground, and then subjected to 700 °C and 900 °C. In this study, various paste and mortar mixtures were produced to investigate the pozzolanic property and environmental impacts of raw WAS and treated WAS at a selected temperature of 700 °C. The pozzolanic activity of both raw and treated WAS at 700 °C was verified using several tests, including X-ray diffraction (XRD), Frattini test, strength-based evaluation, and thermal analysis. The calcium-silicate-hydrate (C-S-H), portlandite (Ca(OH)2), calcium silicates (C2S and C3S), and calcite (CaCO3) were identified as major reaction products indicating the participation of raw or treated WAS. While the reduced [CaO] concentration and location below the solubility curve confirmed the pozzolanic activity of both powders, the compressive strengths of blended mortars were also found greater than 75% compared to the reference mortar at all testing ages. Treated WAS demonstrated higher pozzolanic activity than raw WAS due to the reduced formation of Ca(OH)2 revealed by thermal and kinetic analysis at different time periods. Life cycle assessment resulted in the reduced CO2 emissions by the blended mortars containing either raw or treated WAS, which suggest their promising mechanical and environmental benefits.

Binary and Ternary Blended Portland Cements Containing Different Types of Rice Husk Ash.

Rice husk ash (RHA) is agricultural waste with high silica content that has exhibited proven technical feasibility as a pozzolanic material since the 1970s. Notwithstanding, its use in mortars and concrete is limited by the standards currently utilized in some countries where RHA production is high and the aforementioned pozzolanic material is not standardized. This is the case in Spain, one of the main rice producers in Europe. Nowadays, the high pressure placed on the Portland cement production sector to reduce its energy use and CO2 emissions has given rise to a keen interest in mineral admixtures for cement manufacturing. In this research, we intended to establish the contributions of different RHA types to the final blended Portland cement properties ("H" is used to identify RHA in standardized cements). The experimental results demonstrated that RHA with good pozzolanic properties (large specific surface and high amorphous silica content) had to be limited to 10% cement replacement because of the severe reduction in workability at higher replacement percentages. RHA with lower reactivity, such as crystalline RHA, or fly ash (FA) can be used to prepare binary and ternary blended cements with reactive RHA. It is possible to design the following cements: CEM II/A-H and CEM II/A-(H-V). It would also be possible to design cement (CEM II/B-(H-V) with replacement values of up to 30% and the same 28-day mechanical performance as observed for the Portland cement without mineral addition.

Microstructural Assessment of Pozzolanic Activity of Ilmenite Mud Waste Compared to Fly Ash in Cement Composites.

This paper presents the influence of adding rinsed ilmenite mud waste (R-MUD) on the microstructure of Portland cement composites, compared to similar composites containing fly ash (FA). The aim of the study is the assessment of the pozzolanic activity of ilmenite mud waste by its impact on the microstructure of the cement matrix in comparison to the undoubted pozzolanic activity of fly ash. The presented test results include pore size distribution, phase composition, pozzolanic activity using thermal analysis, R3 bound water test, and microstructural analysis using scanning electron microscopy (SEM). Tests were performed on mortars cured for up to 360 days. The results presented in this paper have shown that R-MUD has a pozzolanic activity level similar to FA or better, which influences pore size distribution in the composite and its microstructure. During the curing process, the microstructure of composites containing R-MUD became more compact and sealed than those with FA, which might also increase their durability. The results of the R3 tests have proven the pozzolanic activity of R-MUD but its level was lower than FA. R-MUD might be a useful substitute for fly ash, especially given the lack of good-quality fly ash on the market.

Utilization of Recycled Brick Powder as Supplementary Cementitious Materials-A Comprehensive Review.

Over the past two decades, extensive research has been conducted to explore alternative supplementary cementitious materials (SCMs) in order to address the environmental concerns associated with the cement industry. Bricks, which are frequently preferred in the construction sector, generate a lot of waste during the production and demolition of existing buildings, requiring environmentally sustainable recycling practices. Therefore, many studies have been carried out in recent years on the use of brick waste as supplementary cementitious materials (SCMs) in cement mortar and concrete production. This critical review evaluates the impact of waste brick powder (WBP) on the mechanical and durability properties of mortar and concrete when used as a partial replacement for cement. It was observed that the properties of WBP-blended cement mortar or concrete depend on several factors, including WBP particle size, replacement ratio, pozzolanic activity, and mineralogical structure. The findings indicate that WBP with a particle size range of 100 µm to 25 µm, with a maximum cement replacement level of 10-20%, exhibits a positive impact on the compressive strength of both mortars and concretes. However, it is crucial to emphasize that a minimum curing duration of 28 days is imperative to facilitate the development of a pozzolanic reaction. This temporal requirement plays a vital role in realizing the optimal benefits of utilizing waste brick powder as a supplementary cementitious material in mortars and concretes.

Resource utilization of stone waste and loess to prepare grouting materials.

Loess, a terrestrial clastic sediment, is formed essentially by the accumulation of wind-blown dust, while stone waste (SW) is an industrial waste produced during stone machining. Utilising loess and SW to prepare environmentally-friendly supplementary cementitious materials can not only address environmental issues caused by solid waste landfills but also meet the demand of reinforcement of coal-seam floor aquifer for grouting materials. In this paper, the effects of the loess/SW mass ratio and calcination temperature on the transformation of calcined products are investigated and their pozzolanic activities are evaluated. The workability, environmental impact and cost of grouting materials based on cement and calcined products are also assessed. Experimental results reveal that higher temperatures favour the formation of free lime and periclase, which tend to be involved in solid-state reactions. Higher temperature and loess/SW mass ratio strengthens the diffraction peaks of dodecalcium hepta-aluminate (C12A7), dicalcium ferrite (C2F) and dicalcium silicate (C2S). The clay minerals in loess become completely dehydroxylated before 825 °C, generating amorphous SiO2 and Al2O3. Covalent Si-O bonds are interrupted and that disordered silicate networks are generated in the calcined products, which is confirmed by the increased strength of the Si29 resonance region at -60 ppm to -80 ppm. Although co-calcined loess and SW contain the most four-fold aluminium at 950 °C, recrystallisation depresses the pozzolanic activity. Hence, the loess/SW sample designated LS2-825 exhibits the better hydration activity. Additionally, grouting materials composed of cement and LS2-825 exhibit good setting times, fluidity, strength and a low carbon footprint in practical engineering applications, and they also provide the additional benefit of being cost effective.

Effect of two different crystal forms of alumina on hydration properties and mechanical properties of steel slag-cement composite cementitious materials.

In the present work, two common nano-alumina (NA) with different crystal forms (α-NA and γ-NA) are used to research the effects of steel slag-cement composite cementitious materials, which include the hydration properties and mechanical properties. The results show that the NA can enhance the strength of steel slag-cement composite cementitious materials, especially the early strength. Meanwhile, when the addition amount of γ-NA was 1%, the maximum compressive strength and flexural strength at 28 d were 35.43 and 5.21 MPa, respectively; when the addition amount of α-NA was 3%, the maximum compressive strength and flexural strength at 28 d were 36.27 and 4.89 MPa, respectively. In addition, according to the analysis of X-ray diffractometer and differential thermal analysis, it was concluded that the effects of the two types of alumina on the strength were mainly pozzolanic effect and filling effect. The pozzolanic effect of γ-NA was significantly stronger than that of α-NA. However, the large surface area of γ-NA affected the dispersion of the particles and the filling effect. According to scanning electron microscope analysis, compared with α-NA, γ-NA had significantly more hydration products and tighter adhesion. In conclusion, the addition of NA not only improved the properties but further realized the value-added utilization of steel slag.