Utilization of Glass Waste as Fine Aggregate Replacement and Rice Husk Ash as Cement Replacement in Concrete: A Review

Cement as a binder used in the mixture of concrete is a costly product and it is also harmful to the environment due to the emission of huge amounts of CO2 and other gases. Like cement the fine aggregate is also the main constituent of the concrete used as inert filler in concrete is also expensive. The researchers are probing towards the new inexpensive and environment friendly materials for the concrete. They have agreed over the point that by utilizing the recycled waste materials could be helpful in achieving the sustainable construction. So in this case a lot of research has been carried out for the utilization of rice husk ash as cement substitution and recycled waste glass as alternative of concrete fine aggregate. The outcome of this research is that these both green materials have enormous potential to contribute in the long-lasting handling of ineffectual solid waste, reduction of landfill sites, preserving natural resources and protecting atmosphere from extremely hazardous gases. The purpose of this review work is to summarize the previous research findings on utilization of rice husk ash and recycled waste glass as a substitution to the cement and fine aggregate respectively. This review paper will come up with the remarkable idea and valuable information for the upcoming researchers working for the aim of utilization of renewable and futile materials in the field of concrete technology.


Introduction
We are using modern concrete since middle of the 19th century but as long as two decades researchers have shifted their focus towards the utilization of supplementary pozzolanic products in the concrete. The reason behind shifting of centre of attention is the sustainability of the concrete and cement manufacturing industries. The production of concrete per year is 10 billion cubic meters. The concrete industry is the largest consumer of key building materials such as cement and natural sand. The world's most populated country China only generated around 2.2 billion metric tons and the India another thickly populated country produced around 320 million metric tons in the year 2019 (Morrin 2003). The statics shows that China is producing over half of the world's cement. It is expected that the global cement production will touch the land mark of 4.83 billion metric tons in 2030 (Morrin 2003). The production of cement causes emission of carbon dioxide (CO2) (Datis Export Group 2020), an influential greenhouse gas. The production of only one metric ton of ordinary cement emits one metric ton of CO2. The amount of emission is about 8% of global CO2 emissions. According to the Paris Agreement on climate change, the member countries agreed to reduce the annual discharge of CO2 up to 16% by the year 2030 (IEA 2017). The reduction in emissions of carbon dioxide and construction cost can be possible if some by-products are used in the concrete. One of the major crop of the world is the Rice (Oryza sativa: Scientific name of rice).The global rice production in 2016 would be around 745.5 million tons as shown in figure 1. Major production of rice is in Asia and pacific regions (Datis Export Group 2020). It is around 11% of the total world's cultivated land. The rice grains are naturally surrounded by a protecting sheath known as hull or husk (Datis Export Group 2020). The world's paddy production in 2018 was forecasted that the global production which has 10.3 million tons annual expansion will touch a peak of 769.9 million tons (510.6 million tons, on milled basis) as shown in figure 2 and 3 (Anand and S 2015).

Previous Research
The summary of literature review has been presented in Table 1. It specifies the previous research findings on the incorporation of RHA as cement substitution and RWG as fine aggregate replacement in the concrete. The researchers and scientists have reconnoitered that the RHA has great capability to perform as a Pozzolanic material, it can be assumed as a replacement of cement for the normal and high strength concrete. In the same way it has been analyzed that the concrete prepared with RWG is competent enough to provide long term strength, stability and good thermal insulation. Therefore, acquiring of these both materials can reduce the cost and environmental issues and will provide a sustainable solution to the construction industry.

Discussion on Previous Findings
Additional cementitious materials are being used to enhance the properties of fresh and hardened concrete. Rice Husk Ash is one of such materials but is still not fully applicable in the construction industry. The above mentioned researches and studies Table 1 tried to investigate the effects of RHA on the different properties of fresh and hardened concrete. In a study when cement was replaced by RHA having specific gravity of 1.89 in proportions of 20% to 50% the effect on compressive strength was not enough but at later ages of 60 days curing at 20% inclusion of GRHA having specific gravity of 2.24 it was improved and at 50% incorporation of GRHA the resistance to chloride penetration increases and steel corrosion reduces (Rattanachu et al. 2020). In another study when the cement was incorporated with the GRHA by 20% and 35% the results exhibited the strength enhancement (Jongpradist et al. 2018). RHA is compatible with CEM II B-LL 32.5 R cement [14] and it has been revealed that the material has good mechanical behaviour in terms of compression and tensile and thermal characteristics. The RHA has good shear performance and the punching-bending test proved that the inter joists are very strong. The study also exhibits that the RHA composite could be used load bearing walls, partitions, false ceilings and inter joists (Chabi et al. 2020).
In case of replacing sand with recycled waste glass powder various tests were conducted on the hardened concrete to find out the compressive strength, split tensile strength and modulus of elasticity of concrete. No major change found in compressive strength of mix. The split tensile strength value decreases with increase in replacement proportions [4]. If the source of glass waste is lighting material the microscopic analysis showed the flat shape causing the accumulation of air beneath the grains in the concrete mix (Drzymała, Zegardło, and Tofilo 2020). In case of CRT glass the densities increases because of low water absorption (Song et al. 2019). The workability of fresh concrete decreases in case of discarded beverage glass due to sharp edges (Bisht and Ramana 2018), but when Metakaolin is used as a cementitious material and CRT glass is incorporated the flow ability is increased (Ouldkhaoua et al. 2020).

Physical and Chemical Properties of Rice Husk Ash (RHA):
Hard protecting coverings of the rice grains are known as rice husks.

Alkali-silica reaction (ASR)
Alkali-silica reaction (ASR) is broadly known as "Concrete Cancer" is an injurious swelling reaction that takes place in the concrete mix containing the alkaline cement paste and the reactive amorphous silica which is mostly present in the moist aggregates with the passage of time. The ASR cause cracking, spalling and reduce the strength of concrete. It is observed that the expansion due to ASR increases with increase in CRTG (Duggal 2008). The highest expansion observed at 28 days curing with 50% replacement as shown in Figure 1.The increase in ASR expansion is due to the presence of higher SIO 2 /CaO ratio (Food and Agriculture Organization of the United Nations 2018). The incorporation of MK up to 10% and 15% was still within the prescribed limit of 0.1%, this is because of the pozzolanic reaction which minimizes the SiO 2 /CaO ratio.

Conclusion
This study The utilization of Rice husk ash as a cementitious material and recycle waste glass as fine aggregate in the construction and infrastructure industry offers an energy saving, environmentally friendly and sustainable alternatives to the cement and natural sand. Upon reviewing the published literature on RHA and Recycled Waste Glass utilized in concrete, the following conclusions can be drawn: VOLUME 20 │ NUMBER 2 │ JANUARY 2021 https://ejournal.worldconference.id/index.php/neutron E-ISSN: 2685-3272 | P-ISSN 1412-0860 The RHA is utilized as a partial cementitious material in the normal, self compacting and high strength concrete and it proved low shrinkage and permeability, high strength, high resistance to carbonation, sulphate, and acid attack.
The grinding time of RHA depends upon the source from where you accumulate it but minimum recommended mechanical grinding time is around 30 minutes to get desirable properties of ash. The chemical composition of RHA varies it is dependent on the incineration process. It contains high amorphous reactive silica the desirable percentages of amorphous silica can be obtained by fully controlled incineration of RHA that is around 7000C.
The proper mechanical grinding of RHA for finer particles can enhance the properties and those properties play an important role for the pozzolanic reaction with other cementitious materials. That grinding time is around 30 minutes for desirable results. It is proved that the untreated rice husk is compatible with CEM II B-LL 32.5 R cement. It has good thermal characteristics and shear performance. The proper curing is essential for the density, microstructure and strength of concrete. The higher age curing such as 28 days and beyond develop a high pozzolanic reactivity and boost the formation of additional C-S-H gels.
From the analysis of above mentioned researches it is revealed that the replacement level of RHA should be around 30% to 35% with lesser size particles up to 20 µm because at higher levels of replacement, the strength reduced due to presence of voids. At 30% replacement the mix will be denser and there will be reduction in water absorption.
The analysis and study of the previous different research articles in which the recycled waste glass is used as substitute to the natural sand as fine aggregate evaluated the following main findings. Because of the similarity in the chemical composition and physical structure of the recycled waste glass powder we found no significant discrepancy in the mechanical properties of the concrete after adding different proportions of the recycles waste glass as an alternative to the natural sand. The different tests were conducted on the hardened concrete to find out the compressive strength (IS 516-1959), split tensile strength (IS 5816-1999) and modulus of elasticity (IS: 516 -1959) of concrete. No major change found in compressive strength by replacing sand with recycled waste glass powder. The split tensile strength value decreases with increase in replacement proportions. The apparent strong point of using the recycled glass powder is the negligible water absorption capacity, which causes no change in the workability.
It is found that recycled tube light waste glass can be used as coarse aggregate in the concrete. A mixture containing 30% by weight has parameters that make it feasible as a construction material. In case of CRT waste glass used as replacement of fine sand it was evaluated that the hardened density, water absorption and damping ratio would decrease when max: particle size is minimized from 0.45mm to 0.60mm on the other hand the compressive strength, tensile strength and elastic modulus and UPV would decrease.
When 50% inclusion of CRTG as fine aggregate and 10% Metakaolin as cementitious material is used the increase in workability, UPV and compressive strength in concrete mix is observed. The chloride ion permeability resistance is observed much higher. It is proved that the MK and CRTG are beneficial for durability. The SEM analysis indicated that the incorporation of MK and CRTG up to 15% can increase porosity due to pozzolanic effect of MK cementitious material which assists in hydration process.
In case of discarded beverage glass, the compressive strength has no substantial growth but was noticed at inclusion of 21% and it was noticed that flexural strength and water absorption increases and bulk density of the concrete mix decreases.

Gape of Study
This review covered the current practice and guidelines of RHA-blended concrete. Simultaneously, this review also revealed a gap in in-depth investigations about the long-term durability and serviceability of reinforced RHA-blended concrete. It was observed that limited research has been done on waste glass as coarse aggregate (Tube light glass).
It causes damage to the vehicle tires when used in the rigid pavements.Tube light glass has phosphor which is harmful to the environment and cause damage to the skin. There should be a study in which recycled waste glass should be used in both forms as fine and coarse aggregate. VOLUME 20 │ NUMBER 2 │ JANUARY 2021 https://ejournal.worldconference.id/index.php/neutron E-ISSN: 2685-3272 | P-ISSN 1412-0860 Seismic performance of the structures made up with the partial replacement of recycled glass waste and rice husk ash should be studied.
The findings of previous studies shows that the use of RHA as cement replacement is for normal strength concrete mixes but there is a need of detailed study especially on high strength concrete mix by utilization of RHA and its durability and other parameters should also be investigated in the aggressive environment.
The impact of seawater on the performance of concrete incorporated with partial replacement of cement with rice husk ash and recycled waste glass as fine aggregate.