Sustainable Development of Pavement Quality Concrete Utilising Fly Ash and Copper Slag

Abstract

Cement concrete pavements are widely used for the construction of durable pavements. The paving industry in general faces problems of increased cost and availability of ingredient materials from natural resources. In modern pavement construction projects, the key priorities in today's world are conservation of natural resources, sustainable development, and reduction of environmental issues. Construction materials have a significant impact on sustainability due to the large demand for raw materials. The use of waste and recycled materials reduces natural resource usage. Utilising industrial waste in construction sectors reduces waste disposal difficulties, pollution, and cost of materials. Due to sustainability concerns, the construction sector is urged to utilise waste materials. In this context, waste materials like, fly ash, blast furnace slag, steel slags etc. have been investigated for their effective utilisation in cement concrete pavement. However, existing study merely explain the effects of combinations of such waste materials on the performance of cement concrete pavement. Thus, the present study is motivated to investigate the combined utilisation of fly-ash (FA) produced from coal-based power plants and copper slag (CS) produced from copper industry in making pavement quality concrete (PQC) as one of the sustainable solutions for construction of cement concrete pavement. This study is divided into four parts. The first part of the study focuses on the influence of FA concentration (10%, 20% and 30%) as replacement of ordinary Portland Cement (OPC), and CS concentration (20%, 40% 60%, 80% and 100%) as replacement of river sand (RS), on physical, mechanical and microstructural properties of M40 and M50 grade PQC mixes. Forty-eight different PQC mixes of M40 and M50 grades were prepared. The combined effects of CS and FA on fresh and hardened concrete properties such as workability, density, water absorption, and volume of voids, cube compressive strength, split tensile strength, flexural strength, cylinder compressive strength, and ultrasonic pulse velocity (UPV), are experimentally investigated. All mixes containing up to 20% FA and up to 100% CS replacements showed increased strength as compared with that of the respective control mix. However, PQC mixes with 30% FA showed decrease in strength properties with respect to the control mix. The PQC mix containing 20% FA and 60% CS resulted in highest strength properties at 90 days’ curing period. The X-Ray Diffraction (XRD) and scanning electron microscope (SEM) studies were employed for the characterisation of selected PQC samples. Further, multiple linear regression equations were established to predict all strength parameters. The PQC mixes made with FA and CS provide superior strength, reduce waste disposal problems, and preserve natural resources for future generations, making such developed mixes sustainable. The second part of the study focuses on the influence of different FA and CS concentrations on durability and microstructural properties of M40 and M50 grade PQC mixes. Various durability tests of all such PQC mixes included resistance to acid attack, resistance to sulphate attack, resistance to chloride attack, drying shrinkage, accelerated carbonation resistance, chloride resistance, sorptivity, slake durability and abrasion resistance. It was observed that the combined use of FA and CS in PQC mixes helps in reducing mass and compressive strength loss as compared with that of control PQC mixes when exposed to 5% sulphuric acid and 5% magnesium sulphate solution. PQC mixes with up to 20% FA and 60% CS showed less chloride ingress depth as compared with that of control PQC mixes. Beyond the stated concentrations the chloride ingress depth goes on increasing. Incorporation of FA and CS together in PQC mixes helps in reducing the drying shrinkage up to 90 days of drying. The carbonation resistance of PQC increased for PQC mixes with combined use of FA and CS. PQC mix with FA and CS showed better resistance to chloride ion penetration. Sorptivity value of PQC decreased with use of 20% FA and 80% CS. Addition of FA and CS improved the slake durability and abrasion resistance of PQC mix. The third part of the study focuses on the flexural fatigue performance of M40 and M50 grade PQC mixes containing varying quantities of FA and CS. For this study the PQC samples (100 mm × 100 mm × 500 mm) were prepared for 90 days’ flexural strength and fatigue life. A servo-hydraulic flexural fatigue testing apparatus was used for determining the fatigue life of PQC samples under four-point bending. A constant frequency of 1 Hz and stress ratios of 0.7, 0.8 and 0.9 were used for fatigue testing. The fatigue characteristics of PQC samples were evaluated in terms of fatigue life distribution. Three methods were used to estimate the Weibull distribution’s parameters. It is observed that the two parameters- Weibull distribution was fitted for the fatigue life distribution of both M40 and M50 grade PQC mixes made with FA and CS. Different failure probabilities have also been considered to estimate the fatigue of PQC mixes. Fatigue characteristics of paving concrete are found to have improved with use of FA and CS as replacement of cement and fine aggregate. The fourth part of the study focuses on the influence of different FA and CS concentrations on economic and environmental implications of M40 and M50 grade PQC mixes for construction of cement concrete pavement considering a typical example problem. The pavement slab made with M40 and M50 grade PQC mixes with FA and CS required a lower design thickness than that with control PQC mixes. For a constant design thickness, adding only CS to PQC mixes raised costs by up to 3.3% over the cost of the control PQC mix. However, PQC mixtures containing both FA and CS reduced the cost by up to 11.5%. The cost of the PQC pavement slab was analysed using the designed thickness and 1 Km length of pavement. It is observed that the PQC mixes containing waste materials having 20% FA and 60% CS (4F2c6 and 5F2c6) can reduce the PQC pavement slab cost by 34.2% and 28.5%, respectively, when compared to the pavement with control PQC mix. By incorporating FA and CS into PQC, the environmental parameters such as global warming potential (GWP) and embodied energy (EE) were reduced by 27% and 25.8%, respectively. It is concluded that using FA (20%) and CS (60%) results in the development of both M40 and M50 grade PQC mixes with superior strength, durability and fatigue properties along with most savings in cost. The approach of utilisation FA and CS can also offer environmental advantages by reducing environmental impact and minimising waste disposal issues. Additionally, it provides economic benefits by reducing costs and societal benefits by preserving natural resources for future generations. Therefore, the PQC utilising FA and CS can be sustainable and suitable for concrete pavement applications.