Alkali Activated Concrete Incorporating Recycled Aggregate and Dredge Marine Sand

Abstract

Buildings made of concrete have been proven to be safe and durable. However, in recent years, concerns about global warming and carbon emissions have intensified. The building sector, particularly cement manufacturing, contributes significantly to worldwide CO2 emissions. According to reports, cement manufacturing contributes to 5-8% CO2 emissions globally. There are various ways to reduce these carbon emissions and one of these is the use of alkali-activated concrete (AAC) and recycled product. Industrial waste like Slag and fly ash activated concrete using sodium hydroxide and sodium silicate have shown excellent strength and chemical resistance. As we know, aggregates play a vital role in concrete, taking up about 60-75% of the total concrete volume. Due to high volume occupied by aggregates in concrete, its need is increasing every day. To overcome this problem, the use of recycled aggregates can be modified into a natural blend by improving its essential properties. Reconstituted aggregates are produced from the processing of previously used building materials such as construction and demolition of building waste, waste aggregate obtained from laboratory samples, concrete from already mixed concrete plants, and pre-disposable units by other sources of recycled components. Reducing the source of natural integration needs to find another way. Sand is an important component of concrete commonly found in alluvial rocks or rivers. Excess sand dredging from the river has become harmful to the environment due to the depletion of the sand layer. Therefore, it is essential to find an alternative that can serve as a long-term sand shift. To prevent this problem, research is continuing to investigate the suitability of dredged marine sand (DMS), coastal sand, and dune sand instead of the river sand. Experimental investigation was conducted using the use of recycled aggregate (RA) as replacement of coarse aggregate and dredged marine sand as replacement of natural river sand by 10%, 20%, 30% and 40% during concrete casting. Tests like fineness modulus, specific gravity, water absorption, moisture content were carried out on all the aggregates. Evaluation of mechanical properties such as compressive strength, flexural strength, split tensile strength, Modulus of elasticity and durability properties such as Sulphate, Chloride exposure, water infiltration, and RCPT were carried out. After exposure to all chemicals, changes in strength and weight change are observed and studied in durable structures. There was a higher decrement in compressive strength due to the incorporation of recycled aggregate in both, AAC and ordinary concrete (OC). However, compared to OC, the decrease in compressive strength in AAC was lesser at 28 days. Flexural strength of AAC when compared with OC decreases by 12%, 19%, 16% and 22% and split tensile strength of AAC decreases by 6%, 7%, 9% and 11% compared with OC at 10%, 20%, 30% and 40% of natural aggregate with RA respectively. Change in modulus of elasticity in AAC decreases marginal when RA proportion increases. It is observed that for ordinary concrete with DMS10, DMS20, DMS30 and DMS40 compressive strength at 28 days decrease by 6.3%, 7.5%, 13.9% and 28.1% and flexural strength at 28 days increase by 7.25%, 6.52%, 7.97% and 10.14%.While for ordinary concrete with DMS20 and DMS30 split tensile strength at 28 days increase by 0.73% and 5.92%.So concrete incorporating dredge marine sand shows the better results. It is observed that in sulphate and chloride attack AAC concrete shows higher change in weight and strength compared to ordinary concrete because of more number of voids and crack present inside it. While ordinary concrete with dredge marine sand shows better results because of densely packed material. Alkali activated concrete with RA10, RA 20, RA30 and RA40 shows change in water penetration by 6.48%, 14%, 21.11% and 22.9% compared to ordinary concrete. Similarly, OCRA40 shows 2430 Q and AACRA40 shows 8019 Q. So it can be concluded that AAC which shows higher chloride ion permeability compare to ordinary concrete because of more number of voids present in concrete. After that when AAC concrete having 30% recycled aggregate compared with ordinary concrete found out to 10% cheaper and also it will use 30% less water. When carbon emission comparison is done, it is found out that AACRA30 shows 41% less carbon emission compared to ordinary concrete because of usage of recycled aggregate. So for non-structural concrete AAC with 40% replacement can be recommended as it will be environment friendly and economical.