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Performance of high‑strength green concrete under the influence of curing methods, volcanic pumice dust, and hot weather

Zeyad Abdullah M., Magbool Hassan M., Amran Mugahed, Mijarsh M. J. A., Almalki Ali

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 3

art. no. e134

This study aimed at examining the impact of concrete curing methods in hot-weather regions on the properties of high-strength green concrete (HSC), which is made from a local industrial waste by-product from the manufacture of light volcanic aggregates called volcanic pumice dust (VPD). The HSC properties are significantly affected by the curing methods, the ambient weather, and the alternative materials to cement. This study aimed to apply three curing methods in a hot-weather region, including the following: (1) the specimens were immersed in a water tank in laboratory conditions, (2) the specimens were cured by covering them with a wet burlap outdoors and spraying the burlap with water twice a day, and (3) the specimens were cured by spraying with water outdoor. Three VPD replacement rates are applied, namely 10%, 20%, and 30% cement mass replacements. In this study, slump tests were conducted and the water absorption, sorptivity, and compressive, indirect tensile, and flexural strengths were investigated to determine the HSC properties. The microstructure of the cement paste was evaluated through thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction. The addition of VPD contributed to reducing the negative impact of hot weather on concrete and improving construction applications. All tests were conducted on hardened concrete at 7, 28, 90, and 180 curing ages. Furthermore, the compressive strength of the immersion curing methods using 10% of VPD surpassed 60 MPa at the 28-day curing age. The residual compressive strength was in the range of 85.6-98.2% when CC and SC were applied compared to IC for all replacement rates at a test age of 180 days. The HSC containing 30% of VPD showed low water sorptivity and water absorption in all curing methods.

Performance and microstructure analysis of high‑strength concrete incorporated with nanoparticles subjected to high temperatures and actual fires

Tobbala D. E., Rashed A. S., Tayeh Bassam A., Ahmed Tamer I.

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 2

art. no. e85, 1--9

Currently, nanoparticles are used as admixtures to reduce the thermal deterioration of concrete after exposure to fire. How-ever, the influence of high temperature on high-strength concrete (HSC) containing silica fume and nanoparticles has not been investigated well. In this study, various HSC mixes incorporated with 1%, 2%, 3% and 4% nanosilica (NS) or 1% and 2% nanoferrite (NF) were prepared to produce HSC with high enduring strength after being subjected to high temperatures of up to 800 °C and actual fires. The specimens were assessed via scanning electron microscopy, compression and splitting tensile tests, modulus of elasticity test, and water permeability coefficient analysis. Results showed that using NS and NF percentages of up to 3% and 2%, respectively, in HSC improved the mechanical properties and water permeability coefficient at elevated temperatures. The compressive strength of the heated specimens with 3% NS was better than those with 2% NF at temperatures 200°C 800°C. With regard to the microstructure feature, the results confirmed that NS acted as an adequate filling material, which produced a condensed microstructure with extra compressed hydration outputs. This may be associated to higher pozzolanic reaction of NS with high distribution that formed additional calcium silicate hydrate gel. The specimens with 3% NS had no cracks until the temperature of 800°C, but their porosity increased slightly.