Kamal, Sirwan (2021) Performance of concrete cured using a curing compound and treated with admixture or surface treatment. (PhD thesis), Kingston University, .
Abstract
Water curing is widely used to maintain sufficient moisture content within concrete. However, curing process could be challenging and difficult in regions suffering from clean water scarcity, or improper curing could occur due to poor site practices. Another method of curing is applying curing compounds (CC) on concrete surface, which creates a protective layer on the concrete surface to prevent or mitigate moisture evaporation from concrete surface. Thus, it retains the amount of water needed for the hydration process. Efficiency of using curing compounds for concrete curing have been investigated by numerous researchers. However, the majority of previous studies focused on the impact of curing compounds on the compressive strength development, rather than transport and durability properties. It is well known that failures in concrete mostly occur due to durability problems such as steel corrosion rather than strength issues. Moreover, many researches have been conducted to evaluate the influence of using protective materials such as waterproofing admixtures (Admix) and water repellent surface treatment (ST) to improve concrete performance. Nevertheless, all previous studies were performed on concrete conventionally cured in water. This study investigates performance of concrete cured using a water-based curing compound and protected by means of waterproofing admixtures or surface treatments compounds. Moreover, mineral admixtures such as fly ash (FA), ground granulated blast furnace slag (GGBS) and silica fume (SF) were added to the mixes to further enhance concrete performance while exposed to aggressive environment. Equal strength plain (CEM I) and binary blended cements were prepared by replacing 20%, 40% and 10% of cement mass (PC) with FA, GGBS and SF respectively, to produce CEM II/A-V, CEM III and CEM II/A-D according to BS EN 197-1. Ultimately, concrete performance was enhanced by the combined effects of waterproofing admixtures or surface treatments along with mineral admixtures. In this study, two set of protective materials in the form of waterproofing admixtures and surface treatments were used. Admixtures were added directly to the concrete batch during mixing, whereas surface treatment agents were applied on concrete surface after curing. Both set of materials provide protection by means of crystalline pore blockers actions, or by hydrophobic effects. This study was conducted in three phases, Phase 1 involved evaluation of engineering properties of concrete specimens cured using the curing compound. To assess efficiency of the CC, v compressive strength, flexural strength and drying shrinkage tests were conducted and results were compared to two set of control samples cured in air (AC) and in water (WC). Phase 2 involved assessing transport properties of concrete specimens cured with CC, and treated either with waterproofing admixtures or surface treatment agents to improve resistance to water ingress. Short-term and long-term water penetration due to capillary absorption and applied pressure were assessed through initial surface absorption test (ISAT), sorptivity (capillary absorption) and depth of water penetration under pressure tests. In Phase 3, durability properties were investigated by conducting carbonation, resistance to scaling and resistance to chloride penetration tests. Results have shown that cubes cured using the curing compound developed more than 93% and 96% of the target compressive strength at 28 and 90 days respectively. Strength development due to pozzolanic reactions was more evident beyond 28 days. Moreover, incorporation of mineral admixtures reduced shrinkage strains under all curing conditions compared to CEM I prisms. In addition, the study has demonstrated that treatment with protective materials particularly those governed by hydrophobic effects, significantly reduced sorptivity due to capillary absorption, and considerably improved resistance to scaling and chloride penetration. Furthermore, the research has established that application of surface treatment agents provided better protection for concrete than addition of waterproofing admixtures. The study has indicated that using a curing compound along with an appropriate protective treatment and mineral admixtures, can safeguard concrete exposed to harsh conditions, for instance, concrete pavements, marine structures and bridges. In addition, producing such concretes can reduce the environmental impact of the construction industry, such as carbon dioxide emissions, and excessive consumption of fresh water during curing, while maintaining the essential properties of concrete.
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