Lightweight foamed concrete as a promising avenue for incorporating waste materials: A review

Highlights

• Comprehensive review on integrating waste materials in pre-foamed concrete.

• Utilization of different types of waste as cement and aggregate substitute.

• Effect of various types of waste materials on properties of foamed concrete.

• Foamed concrete is a promising avenue to incorporate waste materials for sustainability.

Abstract

Several million tons of different types of wastes are generated every year globally and this is expected to increase in the future. Most of these wastes are dumped via landfilling or incineration which creates environmental concerns. One of the possible methods of utilizing these wastes is by incorporating them as alternatives to common concrete constituents. In this regard, foamed concrete could provide an excellent medium for incorporating these wastes in a large volume primarily due to low strength requirement of foamed concrete. A significant number of research is carried out to explore the idea of integrating waste materials in pre-foamed concrete. However, the limited knowledge available to recognize the utilization of these waste and the influence on foamed concrete limits the adoption of the concept and further development. Hence, this paper compiles and reviews the usage of various types of wastes such as industrial, agricultural, quarry, and construction industry wastes as a potential replacement for cement and fine aggregate in foamed concrete. Due to the unique composition and the resulting chemical and physical properties, as well as the nature of replacement (either as cement or fine aggregate replacement), each type of waste contributes differently to the performance of foamed concrete. Generally, a non-load bearing foamed concrete with low thermal conductivity, low density, and adequate compressive strength can be produced by incorporating the waste materials. This paper also describes the advantages of incorporating waste materials in foamed concrete compared to conventional concrete and proposes the further development of the concept for future application of a more sustainable and eco-friendly foamed concrete.

Introduction

Foamed concrete or cellular concrete is either a mortar or cement pastes in which air-voids are artificially entrapped in mortar. It possesses low self-weight, high flowability, minimal usage of aggregate, controlled low strength, and excellent thermal insulation properties. A wide range of densities (400– 1850 kg/m³) of foamed concrete can be obtained by proper control in dosage of foam for application to structural, partition, insulation, and filling grades (Amran et al., 2015; Raj et al., 2019). Due to its lightweight and more economical nature, its applications as a lightweight non- and semi-structural material in the construction industry is gaining growing popularity.

As with normal concrete, the production of foamed concrete also consumes cement and sand, which are concerned about sustainability and environmental issues. For instance, one of the most significant sources of greenhouse gases with carbon dioxide emissions is cement industry. The cement industry produced 8% of the total anthropogenic carbon dioxide emissions worldwide. This percentage is rapidly growing since cement production is expected to increase (Gao et al., 2015; Moumin et al., 2020). Sand, on the other hand, is a non-renewable natural resource and it is important to avoid over-exhaustion and depletion. This is considering that the construction industry is one of the largest consumers of this material, being responsible for 60% of materials extracted from the lithosphere (Bribián et al., 2011).

Potential replacements of cement and sand can therefore help to alleviate the above-mentioned issues and transform the construction sector towards a more sustainable one. One of the most popular methods in this regard is the utilization of waste materials as alternative for common concrete constituents such as cement and sand (Mo et al., 2016; Thomas, 2018). Such wastes are available in abundance around the world include agricultural, mining, industrial, municipal, and construction industries waste.

The traditional methods for the management of these wastes are either by dumping off wastes or by recycling. The dumping of these wastes is usually done via landfill or incineration, both of which are costly, as well as creating environmental and health issues. Among the more common problems with landfills are the generation of liquid, windblown debris, and production of extremely hazardous gas which can affect surface vegetation and greenhouse effects. Whereas the incineration method causes gas pollutants which is detrimental to the environment. On the other hand, the recycling of waste is challenging when involving complex products (Abdel-shafy and Mansour, 2018; Babafemi et al., 2018; Ferronato and Torretta, 2019).

Although waste utilization in concrete has been mooted for some time, there are certain limitations such as lower strength and long-term durability concerns which prevent its widespread applications in the construction industry, particularly for concrete structures. In recent years, foamed concrete is increasingly used for non- and semi-structural applications, where the strength is not the prime consideration (Amran et al., 2015). As such, foamed concrete provides an excellent avenue for incorporating a large volume of various types of waste materials as replacement of cement and sand for more sustainable use of materials. Utilization of waste materials in foamed concrete is therefore an attractive option for addressing sustainability and environmental issues regarding CO₂ emission, natural resources exploitation and waste management via the construction industry.

Despite the research carried out to incorporate waste materials in pre-foamed concrete technology, realization of this concept in application is not yet widespread. This is seen as a setback towards encouraging and promoting the concept of recycling waste into sustainable concrete products. Therefore, in an effort to facilitate the uptake of this technology, this review strives to summarize and discuss the outcomes obtained upon utilizing different forms of wastes as cement and aggregate replacement in foamed concrete made using pre-formed foam. This will be particularly useful for reference towards realizing and adopting the concept in different regions, where the availability of types of waste may vary. Hence, this review analyzes the different types of wastes and their respective influence on the properties of foamed concrete, identify the advantages, limitations and lastly to propose future research directions. For this purpose, the review is structured as follows: Section 2 describes the methodology undertaken for the review; Section 3 discusses different category of wastes and their effects on properties of foamed concrete; Section 4 provides discussion on outcomes, advantages, limitations and future studies; Section 5 provides the research implications while Section 6 gives the concluding remarks of the review.