Effects of recycled waste on the modulus of elasticity of structural concrete

The reduction of pollutants is a project for all international environmentally conscious entities, especially with the increasing emission of greenhouse gases into the environment and discharges from waste in uncontrolled landfills. Furthermore, zones existing for landfills are rare, waste consisting of used tires, waste glass, wood ash, construction and demolition waste is generated every day. Those wastes last in landfills for years because they are typically non-biodegradable. The combination of recycled waste in the manufacturing of concrete is reasonable and attractive for several purposes: lowering the consumption of natural materials, decreasing CO₂ emissions into the surroundings due to aggregate extraction, and additionally improving the viability of the construction industry. It is estimated that the annual utilization of virgin aggregates in the concrete mix design is about ten billion tons¹. According to the World Bank², the world annually produces two billion tons of municipal nonbiodegradable waste, of which at least thirty percent is disposed of in an environmentally professional manner. As a result, the environment has been exposed to a tremendous amount of waste material. In addition, the buildup industry consumes a massive amount of virgin materials for the manufacturing of concrete³. The usage of recycled waste aggregates in concrete mix design offers an alternative environmentally friendly and cost effective route⁴. The mining of natural aggregates, the making of cement, and all the manufacturing processes associated with the making of concrete result in the emission of a tremendous amount of CO₂ into the environment. Because of this, the incorporation of recycled waste in the production of concrete represents an extensive step in the direction of a greater sustainable society.

Landfilling is one of the most significant techniques for managing industrial and municipal waste, but it additionally contributes appreciably to ecological pollutants. Further to the probable risks that landfilling poses to groundwater and soil, it additionally triggers the release of poisonous orders and gases in case it is not professionally managed. Methane (CH₄) and carbon dioxide (CO₂) are among the significant greenhouse gases released from landfills⁵. Those discharged orders and gases have an adverse effect on the environmental welfare. The World Health Organization (WHO)⁶ estimates that approximately ninety-one percent of the planet population exists in places wherein air quality surpass desirable limits. The disposal of tires by way of incineration creates enormous amounts of CO₂, benzene, and different poisonous materials due to their notably flammable tendencies. For instance, old tires take at a least a century to disintegrate naturally, causing soil poisoning and the release of chemical compounds, and almost one fourth of discarded tires are dumped in landfills yearly⁷. The recycling is the best and most powerful ecological manner of disposing of this waste. Discarded dumped tires can be grinded into crumb rubber (CR) and included into concrete mix designs⁸. Gerges et. al.⁹ concluded that the optimum percentage of CR replacing sand in the concrete mixture is five percent to keep maximum compressive strength and ten percent to keep the maximum flexural capacity. Huang et al. al¹⁰ predicted an experimental model linking the CR content to concrete compressive strength. Wang and Du¹¹ empirically established that sound, thermal insulation, and anti-noise benefits is resulted from incorporating CR into the concrete mix.

Glass is another non-biodegradable yet a hundred percent reusable waste dumped in landfills. It hypothetically takes a bottle a million years to decompose within the ecosystem, or still slower in case it exists in a landfill. The US Environmental Protection Agency (EPA), indicated that glass accounts for nearly five percent of the yearly landfilled municipal solid, which comprises of six million tons of glass yearly¹². The addition of waste glass in concrete mix design is feasible due to the similarity of the chemical and physical properties of glass and sand¹³. Recently, several papers^14,15,16 have highlighted the advantages and limitations of combining waste glass in concrete.

Construction and demolition waste (CDW) which are debris produced in the process of the renovation, rehabilitation and demolition of bridges, buildings, and concrete road pavements are mostly dumped in landfills. The EPA promotes and identifies CDW as sources that might be utilized in new construction projects, eliminating the requirement to excavate and procedure virgin materials¹⁷. In 2018, the United States accumulated six hundred million tons of CDW, that is greater than double the quantity of municipal nonbiodegradable waste produced, and is generally dumped in landfills with exhaustible volumetric results. Novková and Mikulić¹⁸, indicated that recycled concrete (RC) aggregates produced from CDW can without issues be utilized to replace concrete aggregates, as they constitute almost seventy percent of the overall volume of concrete. This approach results in a most effective way of saving natural resources, and also saves landfill space and decreases expenses when the expense of the recycling procedure is compared to the cost of extraction of natural resources. The advantages of the usage of RC encompass decreasing the cost of moving CDW to the landfill and moving virgin materials to the construction site. It additionally increases the lifecycle of the landfill via reducing the quantity of waste disposed. At the same token, the realistic utilization of RC in concrete is unusual. Numerous researchers have investigated the benefits of the utilization of concrete with RC partially or wholy replacing natural aggregates (NA). Nováková and Mikulić¹⁸, concluded that twenty percent replacement of NA with RC aggregate resulted in no negative impact on the strength properties of concrete. On the contrary¹⁸, it resulted into increase in compressive strength of 5.8% which was accredited to the residual cement contained within the RC. A research performed by Tošić et. al.¹⁹ determined that incoparating financial, environmental and technical elements, structural concrete containing fifty percent RC would be an optimal proposition.

As the planet apprehends that bioenergy presents a method to decrease CO₂ emissions, the energy produced by the way of biomass is progressively changing into a more essential method of producing energy. Timber biomass is taken into consideration as a sustainable source of generating electricity and a precious renewable opportunity to replace exhaustible fossil fuels. Nevertheless, a typical byproduct of this activity is wood ash (WA). WA is a leading health hazard and environmental pollutant due to the absence of any emission management policies that are normally costly²⁰. The method of managing this waste is either incineration or landfilling. Uncontrolled landfills raise the potential for groundwater contamination from heavy metal leaching in WA and result in airborne diseases to nearby residents. Alternatively, combustion will boost the emission of CO₂ into the environment. Siddique²¹ revealed that around seventy percent of produced WA is landfilled, which is considered the main reason to explore methods for the utilization of WA in construction materials. Naik²² indicated that WA has enormous potential to be utilized as an activator and a pozzolanic mineral admixture in cementitious materials. A compressive strength of 46 MPa was obtained from a mixture resulting from the substitution of twelve percent of cement with WA, thus exceeding the strength of the control mix²³.

Recently published scholarly work by Beskopylny et al.²⁴, experiments conducted on the concrete mix in which rubber tree seed shells replaced coarse aggregates, revealed that the modulus of elasticity, reached a maximum value at a replacement ratio of 4%, while when replacing coarse aggregates with a quantity of 6% or more, a decrease in the modulus of elasticity was detected. Additionally, studies conducted by Mohammed and Sheelan²⁵ in which 15% of waste glass powder was utilized as a partial substitute for cement, and (10 and 20%) of crushed waste plastic was utilized as a partial substitute for fine aggregates increased the modulus of elasticity by 6.01% in comparison to reference one. By contrast, replacing sand with plastic for concrete with 15% glass powder led to a decrease of 20% in the modulus of elasticity modulus.

Recently, a comprehensive review of the effects of multiple waste materials replacing normal ingredients in concrete mix design was published²⁶. Accordingly, the benefits and shortcomings of including CR, WA, RC, and Waste Glass as waste materials to replace common concrete mix ingredients on the modulus of elasticity of concrete are investigated. The main novelty of this work is that it explores the combination of up to three different types of recycled waste materials on the modulus of elasticity of structural concrete mix design. As a matter of fact, the primary purpose of this project is to accumulate, scrutinize, and assess the impact of those recycled wastes on the produced concrete modulus of elasticity. This mechanical property was selected due to its significance in designing structures for the serviceability limit state, in which the primary emphasis is the control of crack widths and the minimization of deflections. The novelty of this study is the replacement of a combination of three waste materials simultaneously in a single concrete mix.