Rapid increments in urbanization and construction work have resulted in greater demand for construction materials, i.e., materials for which natural resources and energy are further consumed in order to manufacture, which results in harmful materials such as greenhouse gasses being produced in the process. These consequences harnessed the attention of scientists and governments toward the idea of sustainability or clean production, such as incorporating byproduct waste as a replacement for cement. Although intense research has been done and many developments have been made in the field of sustainable materials, they are still not widely used due to various reasons, such as the high processing costs and the lack of total understanding of the mechanical and engineering properties for these materials. However, according to statistics [1
], civil works and building construction consume around 60% of raw materials extracted from the lithosphere and are estimated to use up to 40% of global energy consumption. Moreover, construction work has been found as one of the highest carbon emissions industries [2
] due to the production, processing, and transportation of construction materials [3
]. Previous studies estimated that 50% of CO2
emissions worldwide come from cement manufacturing sectors [5
]. Recently, the tendency to replace such materials with sustainable admixtures such as waste is growing around the world. Some of the commonly used sustainable admixtures are bottom ash [6
] and marble dust [8
Coal bottom ash is a byproduct produced largely from coal-powered plants; thus, utilizing coal bottom ash in the concrete industry can be an economic and sustainable method for its disposal [10
]. In general, bottom ash is believed to adversely affect the workability of concrete [11
]. However, some published studies reported increased workability when using bottom ash as a replacement of natural sand [13
]. Wongkeo et al. [15
] investigated the effects of replacing Portland cement with BA showing that BA mixes had improved bulk density, thermal conductivity, and flexural and compressive strength. Furthermore, Aydin’s [16
] study on the effects of adding BA to a pure cement matrix showed that composites with up to a 70% replacement of BA demonstrated suitable physical and mechanical properties to be used in construction.
Concrete is the main material used in the growing sector of construction. However, concrete is known for its brittleness, which inspired scholars to search for methods to alleviate this problem. One popular solution is the use of fiber reinforcement in a concrete matrix, which is a toughening material that has the potential to improve compressive strength as well as shearing and fracture resistance of concrete. Over the past years, developments have been achieved and a better understanding of the behavior of fiber-reinforced concrete has developed due to the vast research that was and is still ongoing in this field; more recently, these materials are being fabricated for hydraulic and civil buildings all around the world. Steel, carbon, glass, and polymer [17
] are among the most popular types of these fibers. The most-used type of polymer fiber is polypropylene. The effects of these fibers on cement have been intensively studied. Many researchers [18
] reported an increase in the compressive and flexural strength when adding fibers to cement composites. Valeria and Nardinocchi [18
], for example, observed a reduction in the drying shrinkage upon adding fiber to cement composites. Moreover, Hwang et al. [25
] reported enhanced flexural strength, toughness indices, plastic cracking, and impact resistance from the addition of natural fibers to cement composites.
Basalt fiber is one of the most popular fibers worldwide. It is a material that is usually made from the fine fibers of basalt. This fiber is similar in shape to glass fiber (GF). However, it has better physicochemical properties than GF; further, it has been reported to make better contributions to the properties of concrete [26
]. In addition, the price of basalt is cheaper compared with carbon fiber, which makes it an ideal substitute for carbon fiber. More recently, basalt fibers have been widely used in civil and hydraulic engineering [26
]. Regarding concrete, many studies have been conducted on the behavior of basalt fiber on the durability and strengths of concrete. Khan et al. [27
] investigated the properties of concrete mixes enhanced with basalt and steel fibers, reporting an enhancement on the mechanical properties of concrete up to 0.68% of basalt inclusion. The authors also observed up to a 74% reduction in workability. Sun et al. [26
] also investigated the addition of both short and long basalt fibers to concrete, finding that the compressive and splitting tensile strength of concrete increased with the addition of fiber up to 2% by volume and started to decrease after that, while bending strength kept increasing with increasing the fiber volume. The authors further found that short fibers were more effective in improving the strength of concrete. Sim et al. [28
] reported that basalt fiber performed better than glass fiber under accelerated weathering conditions and provided higher resistance to temperature than that of glass fiber. Gamal et al. [29
] conducted another study concerning the use of basalt fiber in concrete construction. They reported that the use of basalt fibers helped in retaining and improving the strength of concrete that is exposed to vegetable and mineral oils. The basalt-fiber-reinforced concrete could withstand the acidic, chemical, and salty effects that result in the reduction of the strength of concrete. Dong et al. [30
] evaluated the potential of using basalt fibers to enhance the mechanical properties of concrete made with recycled earthquake waste. The authors also found that using basalt fibers can make up for the reduction in mechanical properties when increasing the ratio of waste replacement. Similarly, Wang et al. [31
] suggested the use of basalt fiber with nanosilica to enhance the mechanical properties of recycled aggregate concrete.
Ahmad and Chen [32
] studied the water and high-temperature resistance of mortars containing various proportions of basalt fibers and silica fume. They reported increased resistance by increasing the amount of silica fume and fibers as well as decreased porosity. Padalu et al. [33
] investigated the use of basalt-reinforced mortar for wallettes strengthening. The strengthened wallettes showed four times higher strength, 29 times higher deformability, and 139 times higher energy-absorption capacity. Fenu et al. [34
] also studied the dynamic behavior of mortars reinforced with basalt and glass fibers, investigating their influence on energy absorption and tensile strength. They reported increased energy absorption at high strains with the addition of fibers, while the dynamic increase factor was not significantly affected by the addition of fibers.
In this study, two different percentages of bottom ash (40% and 50%) and three volume fractions of basalt fiber (0.3%, 0.75%, and 1.5%) were used to investigate the physical, mechanical, and durability properties of the laboratory-produced composites. In the literature, to the best of our knowledge, no research consists of pure cement paste enriched with basalt fiber. This study was composed of comprehensive laboratory tests at three curing periods (7, 28, and 56 days). Additionally, the prepared composites were composed of bottom ash at high levels of utilization rate. The composites could be a promising alternative binder in the concrete sector and could be used as alternative novel-based composites. The durability properties of those composites were evaluated based on real-scale conditions. The samples were immersed in a seawater and sulfate solution to check their performance. In the literature, all studies focused on mortar and concrete properties; further, none of them were composed of pure cement paste enriched with basalt fiber. This research will fill the research gap in that particular area.
Basalt fiber can be considered ecological material since it is manufactured from the basalt rock, which is naturally found in the Earth’s crust. Basalt is a natural rock found in abundance all around the world; it is used in the production of basalt fiber under a low-energy intensive process. Due to its high tensile strength and excellent modulus properties, its effectiveness in cement-based composites makes it an ideal candidate in the construction sector. Since it is considered an environmentally friendly material, the authors believe that its utilization will increase in the future. It will help to improve sustainability strategies for all nations. Here, in this study, the basalt-enriched bottom ash cement paste composites have proven their superior performance against sulfate and seawater attack. Additionally, composites have excellent mechanical properties. The use of bottom ash wastes to produce cement paste composites could possibly have a beneficial effect on the environment. The bottom ash used in this study can be considered as a high replacement level for cement (40% and 50%). The authors further believe that the composites can be sustainable and environmentally friendly. The experimental results showed that basalt fiber works well with bottom ash composites.
Although large portions of clays and other natural raw materials are used in masonry-related applications such as manufacturing of bricks, blocks, and paving units, the authors believe that use of natural raw materials consumes our resources; thus, bottom ash can be used effectively and satisfactorily in the building sector to reduce carbon dioxide emissions. Its utilization is still low, however, in the construction industry. Moreover, the use of bottom ash or other industrial waste in such applications, stated or controlled low-strength applications in the construction sector, has great potential in achieving a sustainable building industry and reducing carbon footprints. The authors further believe that using them in structural concrete applications provides a more sustainable approach in the concrete sector. However, more research should be conducted, especially for those applications to check safety regulations.
The authors checked the performance of their bottom ash cement paste composites through various tests such as physical, mechanical, and durability. Additionally, the authors evaluated the bottom ash cement paste composites according to the current international standards and tried to optimize the performance of our composites based on those mentioned tests. Based on the experiments in this study, the following conclusions can be reached:
The addition of basalt fiber improves the workability of the composites at a lower volume fraction. Beyond a 0.3% basalt fiber addition, the decrease in flow values was reported for all mixture groups.
The porosity of the composites increases as the basalt fiber volume fraction increases. The compactability of the fiber is adversely affected beyond 0.3% volume fraction.
The dry unit weight of the composites is classified as light weight. The produced composites have superior physical, mechanical, and chemical stability, which makes them an alternative sustainable construction material. Additionally, the mixture proportioning in this study can help for the development of sustainability strategies in the concrete industry by utilizing bottom ash and basalt fiber as an alternative binder.
The addition of basalt fiber increases the water absorption of both mixture groups beyond 0.3% volume fraction. More cement paste is needed when basalt fiber is introduced into the system. This affects the pore system of the composites.
The addition of basalt fiber increases the compressive and flexural strength. Both strengths tend to decrease beyond 0.75% volume fraction.
The addition of basalt fibers seems to be effective in chemical stability. Basalt fiber improves the resistance of the composites against sulfate and seawater.
Microscopic investigation should be conducted for a better understanding of these novel-based pure cement paste composites, which contain basalt fiber and industrial waste. The authors believe that the formation of calcium silicate hydrates and dispersion of basalt fiber in the matrix governs the overall behavior of the composites and need further investigation.