RESUMO
Polymer compounds have become a popular choice for the synthesis of novel products and are being used in cementitious mixtures principally for altering the properties in the fresh state and as repair materials. These polymers are used in various combinations. Their interaction with cement is worth studying because its hydration, followed by setting and hardening, is the primary phenomenon contributing to the strength gain and performance of concrete. This paper summarizes the effects of different polymers on the hydration of cement and the properties of concrete/mortar. Studies have established that the incorporation of polymers as a workability enhancing admixture or for improving strength, durability, and other properties severely affects the early hydration of cement and reduces the overall strength gain in most cases. The hydration retarding effect depends on the charge, architecture, and the amount (wt %) of polymer added. However, owing to the densification of the interfacial transition zone and formation of polymer films/bridges between stacks of calcium hydroxide surfaces and air, the later age properties show beneficial effects such as higher flexural strength, enhanced compressive strength, and modulus of elasticity, better resistance against frost, and corrosion of steel reinforcement. Further, it is seen that the hydration retardation may be mitigated to some extent by the addition of silica fume or zeolite; using a defoaming agent; curing at high temperatures; and following a combination of wet, moist, and dry curing regimes. This review is expected to be helpful to all practicing civil engineers who are the immediate users of these chemicals and are working to achieve quality concrete construction.
RESUMO
The main goal and novelty of this study is to show the transferability of practices and experiences with the use of reclaimed sand worldwide in the case in two different regions, the Czech Republic and India, which is necessary for both regions due to the sand availability (Czech Republic) and illegal sand mining including criminal offences (India). Due to the deteriorating environmental impacts associated with sand mining, finding substitution possibilities for natural sand is becoming more important worldwide. It is realized that the reuse of construction demolition waste concrete is inevitable in the pursuit of circular concrete and cleaner production, envisioned by the United Nations (UN) as the attainment of ensuring sustainable consumption and production patterns (Sustainable Development Goal 12-SDG 12) with an inclusive approach of partnerships to achieve the goal (Sustainable Development Goal 17-SDG 17) for the validation of results. The basic material properties of reclaimed sand were examined, and its impact on the physical, mechanical, and durability properties of concrete with complete replacement of sand was evaluated. Generally, a slight decline in properties of concrete with fine recycled aggregate was found. No significant decrease was found from usage possibility in the point of view of its utilization in specific structures and conditions. The research shows the slight differences of results between the Czech and Indian investigations, which are not essential for the transferability of the results.