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Processing of calcium sulfoaluminate eco-cement coatings containing microencapsulated phase change materials

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).

Effects of waste magnesia powder as partial cement replacement on self-compacting concrete

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.

Estimation of compressive strength of cement mortars using impulse excitation technique and a genetic algorithm

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.