In the context of green and low-carbon materials development, the influence of replacing cement with circulating fluidised bed fly ash (CFBFA) on the expansion properties of paste under different curing conditions was first systematically investigated. Then, self-compacting concretes (SCCs) with recycled aggregate (RA) and CFBFA were prepared for filling steel tubes. The experimental results showed that, because of its unique physicochemical properties, the incorporation of CFBFA significantly increased the water requirement needed to achieve standard consistency of the paste and the pore structure was optimised by a reduction in the number of large pores due to the formation of more expansion components (ettringite, gypsum and portlandite are the main expansive products of CFBFA–cement paste). The influence of factors such as curing condition, age and CFBFA on the expansion effect was notable. With a 40% CFBFA content, the RA SCC in the steel tube showed an expansion of 41 μm/m, while the 28-day compressive strength reached 48.9 MPa.

On the one hand, calcium sulfoaluminate (CSA) eco-cements release about 40% less CO2 than Portland Cement during fabrication; on the other hand, phase change materials dispersed in a cementitious matrix can help optimise the indoor temperature of buildings, reducing CO2 emissions related to heating/air conditioning. However, this is only economically viable if it is used as a thin layer (a coating). In addition, the combination of both materials supposes a double environmental benefit. Consequently, the main objective of this work is the preparation of a suitable homogeneous and well-adhered bilayer sample, composed by CSA and CSA-MPCM. For that, in the first step, the effect of pH, temperature and stirring was studied for microencapsulated phase change material (MPCM) aqueous suspensions (47.3 wt%); secondly, the MPCM (45 wt% respect to dry cement) was dispersed in a CSA paste; and in a third step, a homogeneous well-adhered coating of CSA-MPCM, with non-destroyed MPCM, was obtained onto a CSA matrix. This was achieved through rheological measurements and checked by microscopy. Finally, the corresponding CSA and CSA-MPCM mortars were characterised through their mechanical properties (compression) (70 and 13 MPa at 7 days, respectively) and thermal conductivity (2.06 and 1.19 W/mK, respectively).

The ultrasonic pitch-catch experiment was conducted to study the hydration behavior of Portland cement paste with additive of sodium gluconate (SG) by using the tailor-made piezoelectric transducer. The X-ray diffraction (XRD) analysis shows that the intensity of the diffraction peak of Ca(OH)2 decreases with increasing the SG content, especially when the SG content is larger than 0.1wt.%. The compressive strength of the hardening cement paste when SG content is larger than 0.05wt.% decreases remarkably. The ultrasonic waveforms appear at hydration age of 2 h, and amplitudes of waveform of the cement pastes with SG contents of 0.15wt.% and 0.2wt.% are obviously larger than those with SG content of 0.05wt.% in the early hydration stage. The hydration process of cement paste in 300 h can be classified into three stages based on the head wave amplitude variation, that is, the fluctuation variation period, the rapid increasing period and smooth increasing period. The acoustic propagation time changes greatly with hydration before hydration age of 48 h, indicating that the hydration and hardening process of the cement paste is violent in 48 h. The proposed ultrasonic monitoring method opens a new perspective for hydration behavior study of the cement paste with additive of sodium gluconate.

This experimental study investigated the performance of self-compacting concrete (SCC) mixes with magnesia waste. In the series produced with the water/binder ratio of 0.40, cement was replaced by magnesia waste as 2%, 4%, and 10% by weight in self-compacting concrete. Le Chatelier test, slump-flow, compressive strength, flexural strength, depth of penetration of water under pressure, ultrasonic pulse velocity, and water absorption by capillary were conducted to assess sample performance. X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury intrusion porosimetry (MIP), differential thermal analysis (DTA), and scanning electron microscopy (SEM- EDX) were used for the microstructural analysis and quantifications of phases within each sample. The results indicated that concrete with magnesia waste contains magnesium silicate hydrate (M-S-H) and brucite ((Mg(OH)2) products. Mg(OH)2 causes strength loss in concrete. Up to 90 days, specimens with MgO showed increasing compressive and flexural strength. As the amount of magnesia waste increased, the porosity, the depth of water penetration under pressure, and the water absorption by capillary increased. Incorporating more than 10% of magnesia waste in the self-compacting concrete mixtures resulted in declining strength. The addition of magnesia waste enhancement the expansion of SCC. An optimum dosage (2%) of magnesia waste was the most advantageous to the strength of self-compacting concrete. Highlights: • Magnesia waste significantly increases the slump-flow value of self-compacting concrete. • Adding MgO and using fly ash improves the early-age strength. • Magnesia waste powder fills the voids in the concrete. • As the curing age increases, the strength of magnesia waste also improves in the self-compacting concrete.

Compressive strength, a crucial mechanical property of cement mortars, is typically measured destructively. However, there is a need to evaluate the strength of unique cement-based samples at various ages without causing damage. In this paper, a predictive framework using a genetic algorithm (GA) is proposed for estimating the compressive strength of ordinary cement-based mortars based on their dynamic elastic modulus, measured non-destructively using the impulse excitation technique. By combining the Popovics model (PM) and the Lydon–Balendran model (LBM), the static elastic modulus of samples was calculated using constant coefficients, representing an equivalent compressive strength. A GA was then employed to determine optimal values for these coefficients. The results showed that the LBM-based strength was dominant in the middle range of the dynamic Young's modulus while the PM-based strength was dominant for higher and lower values of the dynamic Young's modulus. The model was found to have a small root mean square error (3.1%). The findings suggest that this non-destructive model has potential for predicting the mechanical properties of cement mortars. It allows efficient evaluation of compressive strength without destructive testing, offering advantages for reliable assessments of cement-based materials.

Gas conditioning towers (GCTs) or cooling towers have broad industrial applicability, especially in the cement industry. Most cement factories deal with the same problems faced by other factories. However, the solutions to these problems are barely internationally published and have not received much attention, meaning a lot of time and money is spent on researching previous solutions. Iran is among the top ten cement manufacturing countries in the world. Therefore, many of these problems have occurred in Iranian cement factories. The purpose of this paper is to provide a review of studies in this field over the last couple of decades, with a particular focus on advances in Iran. The most important findings in the literature are summarised in order to suggest the best possible solutions for improving the performance and lifetime of GCTs and decreasing common problems such as dust build-up and wet bottom. Numerical methods for modelling different aspects of GCTs are reviewed. The results can be used to reduce water and energy consumption, air pollution and the repair and maintenance costs of cement factories.

Calcium aluminate cement (CAC) is advantageous in marine engineering, and using materials directly from the sea when mixing CAC can reduce both construction costs and ecological pollution to the sea. However, using seawater as the mixing water in CAC is difficult due to the strength reduction. In this work, CACs were prepared with siliceous minerals (SMs) (diatomite and silica fume (SF)) and sodium chloride solution (SCS) as the mixing water. For comparison, other samples were immersed in SCS rather than mixed with SCS. The strength, mass and length changes of CAC mortars cured at 20°C and 40°C were determined. The phase assemblages and morphology were assessed using X-ray diffraction, thermogravimetric-differential scanning calorimetry and scanning electron microscopy. Using SCS as the mixing water was beneficial to the later strength development of CAC. It promoted the formation of C2ASH8 in CAC pastes and showed no strength loss even when cured at 40°C. The strengths of the SM-modified CAC mortars mixed with SCS were higher than those immersed in SCS. The combination of diatomite and SCS significantly increased the CAC strength, especially at 20°C, while SF contributed to better stability in mass and length.

Fly-ash-based geopolymer pastes with the addition of expanded vermiculite (EV) powder were synthesised and their microstructure, compressive strength, setting time, moisture control, extent of efflorescence and thermal conductivity were studied. It was found that the addition of EV resulted in an increase in the standard-consistency water consumption and setting times. As a consequence, excessive addition of EV resulted in a larger amount of harmful pores, which was detrimental for the compressive strength of the paste. However, geopolymer pastes with an appropriate amount of EV (2–7 wt%) showed a slight increase in compressive strength because of the filler effect. Mg2+ and Fe3+ diffused from the EV interlayers through ion exchange between the EV and the geopolymer, and participated in geopolymerisation. This was reflected by the formation of N-(M)-A-(F)-S-H, as evidenced by scanning electron microscopy with energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. In addition, Na+/Mg2+ or Na+/Fe3+ ion exchange reduced the mobility of Na+ the ions and therefore decreased the extent of efflorescence. Moreover, EV addition favoured an improvement in moisture content and the thermal conductivity properties of the geopolymer paste.

A comprehensive semi-empirical model was developed to predict the drying shrinkage strain (DSS) of concrete reinforced with graphene oxide nanosheets (GONs). The model includes various internal and external parameters. The effects of three factors (the age when drying starts, the GON content and aspect ratio) on the DSS of concrete reinforced with GONs were investigated. Compared with the results of other models (CABR, CEB-78, CEB-90, ACI-209, B3 and GL2000 for plain concrete and modified ACI-209 and B3 models for concrete reinforced with GONs), the results of the proposed model were found to be in better agreement with the experimental data. Moreover, several sensitivity analyses were carried out for the DSS of concrete with 0.02, 0.05 and 0.08 wt% GONs as functions of the environmental relative humidity and temperature, compressive strength, cement content, aggregate/cement ratio, sample size, gravel/sand ratio, sand/cement ratio and water/cement ratio. The developed model can not only evaluate the DSS of concrete containing GONs well, but it can also be applied to predict the DSS of cement reinforced with GONs.