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.

Use of industrial by-products as raw materials in concrete is becoming necessary to address the sustainability of both the concrete and the industrial growth. The present study assesses the potential of imperial smelting furnace (ISF) slag as in concrete, considering the presence of toxic elements (lead and zinc) and their detrimental effects on the early hydration of cement. Equivalent volume of sand was replaced by ISF slag in different percentages. Concrete specimens were prepared at different water-to-cement ratios. Compressive, flexural, and pull-off strength, along with abrasion resistance, were examined. Leaching potentials of toxic lead, zinc, and cadmium from ISF slag concrete mixtures were also analyzed to evaluate environmental viability. Results are encouraging because sign of delay in setting was not observed. Improvement in compressive and pull-off strength, comparable flexural strength and abrasion resistance, and leaching of toxic elements within safe limits assures the potential o...

Recycling of materials such as masonry or concrete is one of the suitable ways to reduce amount of disposed construction and demolition waste (CDW). However, the environmental safety of products containing recycled materials must be guaranteed. To verify overall environmental benefits of recycled concrete, this work considers ecotoxicity of recycled concrete, as well as potential environmental impacts of their life cycle. Moreover, impacts related with carbonation of concrete is considered in terms of durability and influence of potential CO₂ uptake. Concrete containing fine recycled aggregate from two different sources (masonry and concrete) were examined experimentally at the biochemical level and compared with reference samples. Leaching experiments are performed in order to assess physicochemical properties and aquatic ecotoxicity using water flea, freshwater algae and duckweed. The consequences, such as effects of material on soil enzymatic activity (dehydrogenase activity), photosynthetic pigments (chlorophylls and carotenoids), and the carbonation process, are verified in the laboratory and included in the comparison with the theoretical life cycle assessment. As a conclusion, environmental safety of recycled concrete was verified, and its overall potential environmental impact was lower in comparison with reference concrete.

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.