No abstract

The use of high chemical admixture dosages in ultra-high-performance concrete (UHPC) mixtures to achieve adequate water demand can slow down early cement hydration and prolong the setting time. In this study, the effects of nanosilica (Ns) with high chemical admixture dosages on the rheological properties of UHPC was investigated. A factorial design approach was employed to predict and optimise the Ns content, water-binder ratio (W/B), and sand-binder (s/b) ratio to obtain the best flowability, setting time, and compressive strength. This study represents an attempt to modelling and optimise eighteen UHPC mixtures containing various proportions of water, cement, and sand, with the Ns powder as a possible property enhancer to achieve the best rheological properties. Response surface analyses revealed the significant effect of Ns in controlling the prolonged setting time and improving the compressive strength. Based on the applied criterion conditions, the optimisation results indicated two mixtures targeting either the maximum compressive strength or cost effective materials. The use of a 1.12 s/b ratio with a controlling level of 0.8% Ns content was suitable to fulfil the compressive strength, flow, and setting time limit values.

No abstract

1.1 BackgroundGlass, with its variety of forms, is a typical amorphous material that whenrecycled for numerous times, it may maintain similar chemical properties. Preliminary examination and pozzalanic activity index testing exhibited compliance with specifications and a potential for use as a supplementary cementitious material. The effects of replacement percentages that ranged from 0-20% by the total binder weight on various fresh, hardened, durability and microstructure properties were investigated. The percent of replacement 20% of glass powder (GP) by the total binder weight revealed the highest results for strength mortar. Expansion due to alkali silica reaction (ASR) reduced considerably with the increased GP content, and a level of 20% GP has exhibited the best ASR resistance. Rate of water absorption was found to reduce with replacements in the range up to 15%, indicating more impedance to capillary water permeability and expected improved durability. XRD results suggest that GP has a positive effect on the consumption of portlandite, especially in the higher percent. An average glass content of 15-20% was found optimal to produce an eco-sustainable mortar where cement is partially replaced with as much waste material as possible, and that achieves high levels of mechanical characteristics.

No abstract