Studies on Strength, Durability, and Structural Properties of Copper Slag Aggregate Concrete

Abstract

Concrete is the most versatile construction material because it can be designed to withstand the harshest environments while taking on the most inspirational forms. Engineers are continually pushing the limits to improve its performance with the help of innovative alternative aggregate and supplementary cementitious materials. Aggregates are usually obtained from natural rocks, either crushed stones or natural gravels, and comprise as much as 60% to 80% of a typical concrete mix. So they must be properly selected to be durable, blended for optimum efficiency, and also should exhibit a good bond with reinforcement after hardening. Initially, these are generally thought of as inert fillers within a concrete mix, but a closer look reveals the major role and influences aggregate plays in the properties of both fresh and hardened concrete. The rapid growth of industrialization gave birth to numerous kinds of industrial slags that are environmentally hazardous and create problems with storage and disposal. The consumption of these slags as a replacement for aggregates in concrete not only helps in saving natural resources but also helps in making environmentally friendly construction material. Hence, the management and utilization of industrial slag have become important for some researchers in the past couple of decades. Presently in India, due to limited modes of practices of utilization, a huge amount of copper slag is dumped in yards of each production unit and engaging important agricultural land and grave pollution to the whole environment. Currently, worldwide about 57 million tonnes of copper slag is generated annually with India contributing 12-16.5 million tonnes. Barely dumped copper slag pollutes the nearby soil and the adjacent water bodies ultimately contaminating groundwater, lakes, streams, rivers, or coastal waters. On the other hand, this copper slag is often mixed into municipal waste and hinders making accurate assessments difficult. An efficient approach to overcome these problems is slag utilization, which minimizes land disposal. The disposal of copper slag is an environmental challenge globally, and the only viable solution for its mass disposal is its use in the construction industry, especially for concrete production. However, the performance of a concrete structure is dependent upon the properties of the components such as cement, coarse aggregate, fine aggregate, and superplasticizer along with several other factors. Physical and chemical characterization of the slag is a deciding factor in its utilization as fine aggregate as recycled construction materials, etc. Basic physco-chemical properties like specific gravity, fineness modulus, particle size distribution, chemical composition, and strength activity index of both copper slag and natural sand are studied. Hence, the evaluation of copper slag aggregate concrete (CSAC) properties is essential for the quality construction of the concrete structure. The present research is an effort to study the engineering properties of CSAC which include strength properties, durability properties, and structural properties, establish the correlation among these properties, and quantify variability associated with different strength properties over a longer curing period of 90 days. Basic fresh concrete properties like workability and rate of bleeding, hardened concrete strength properties like compressive strength, split tensile strength, flexural strength, water absorption, void content, microhardness, and microcrack analysis are studied on a large no of CSAC samples and the obtained result is checked for its appropriateness in eminence construction. Better particle packing and due to the presence of natural pozzolana (Class N) in copper slag which strongly influences all the strength properties. Durability properties like slake durability, abrasion resistance, accelerated corrosion test, rapid chloride penetration test, and carbonation test are also studied on a large number of CSAC samples. Some efforts have been made to test the suitability of copper slag use in designing durable concrete. However, the evaluation of all these strength and durability properties needs admittance to polished instruments, which is normally not obtainable in the majority of construction sites. This demands the development of a substitute technique that could deliver first-hand information on the strength, durability, and quality of CSAC without the need for any huge testing apparatus. For this resolve, the correlation between the strength, durability, and other easily measurable parameters is studied and mathematical models are developed to predict the CSAC properties using other parameters through experimental results and statistical correlation. These models can be used as a quality control tool for CSAC production at the actual construction site. A proper mechanical interlocking between cement and aggregate results in good bond strength of structural concrete. If the aggregate possesses its own pozzolanic property, the interlocking improves due to secondary hydration products on the aggregate surface. Both strength and durability of concrete are influenced by the bond strength to a large degree. The strength properties of CSAC can show a significant variation because of several influencing factors like source and proportion of constituent materials, workmanship, and curing condition among others. Quantification of this uncertainty is essential for the reliability-based limit state design of masonry structures. Safety and strength assessment of structures made of CSAC often requires modelling the uncertainty of its properties. The present study investigates the variability associated with compressive strength, shear-, split tensile-, and flexure tensile-bond strength of copper slag aggregate concrete were analysed and proposes the most appropriate model for its statistical distribution. Four probability distributions are considered to conduct the three goodness of fit tests, namely Kolmogorov-Smirnov, Kolmogorov-Smirnov-Lilliefors, Anderson-Darling, and Chi-Square (CS) tests. The analysis shows that conventionally assumed normal distribution is not suitable for describing the strength properties of copper slag aggregate concrete as the experimentally obtained strength data is not symmetrical about its mean value. The best-fitted distribution functions that perform well in describing the variability in different strength properties of copper slag aggregate concrete are recommended. A case study on the seismic risk of a typical reinforced concrete framed building with CSAC is performed considering different probability distribution functions. The results of the case study indicate that the choice of the probability distribution of the random variables influences the seismic risk assessment of structures significantly and consideration of the appropriate distribution function is vital for the precise estimation of seismic risk.