Mechanical Properties of Concrete Incorporating Rice Husk Ash and Wheat Straw Ash as Ternary Cementitious Material

Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Tronoh, Perak, 31750, Malaysia Department of Civil Engineering, Covenant University, Ota, Nigeria Department of Civil Engineering, ISRA University Hyderabad, Hyderabad, Sindh, Pakistan Department of Civil Engineering, Quaid-e-Awam University of Engineering, Science and Technology Campus Larkan, Nawabshah, Sindh, Pakistan Department of Civil Engineering, Anna University, Chennai 600025, India


Introduction
e use of concrete has been admired for decades throughout the world [1]. Concrete is man-made material prepared by mixing cement paste with fine and coarse aggregates in designed proportions. e construction industry is highly dependent on this incredible material, and for the time being, there is limited availability of resources that include the binding material, i.e., cement, and aggregates, i.e., coarse and fine. Hence, it is necessary to lessen degradation of natural materials and resources [2] by introducing inexpensive and leftover materials possessing pozzolanic properties with the prospect to substitute conventional materials of concrete [3]. Cement is a costly concrete constituent, and its manufacturing discharges huge quantity of carbon dioxide in the atmosphere [4][5][6]; one ton of carbon dioxide is released while manufacturing one ton of cement [7]. To lessen cost of manufacturing and amount of carbon dioxide, researchers are investigating to replace cement partially with agricultural or industrial discards, i.e., blast furnace slags, wheat straw ash, rice husk ash, fly ash, glass powder, and others [7,8]. Moreover, concrete production is also liable to be the source of discharge for greenhouse gases in the atmosphere as yearly concrete production is about 1.6 billion tons, which causes the release of greenhouse gases which account for approximately 7% of total gas emissions [9].
Consequently, effective consumption of solid waste materials in concrete aids in mitigating common problems of environmental pollution, scarcity of raw materials, energy crises, and overhead costs of constructions [10]. Additionally, there could be a major improvement in concrete performance in strength as well as in durability with effective consumption of waste pozzolanic materials, and hence extensive research is being carried out on pozzolans like ashes of sawdust, rice husk, wheat husk, sewage dust, and metakaolin [11], ashes of coconut shell, bottom coal, corn cob [12,13], and so on. Rice husk ash is a solid waste utilized as cementitious material, and bottom coal ash is utilized in replacement of fine aggregate during this research work. RHA, an agricultural by-product [14][15][16] generally burned in open space, is regarded as the source of air pollution [17,18],because it is regarded as a waste product and proper disposal of such kind of waste is a serious concern as 120 million tons of rice husk is thrown away or burned annually [19][20][21]. RHA contains about 85% of amorphous silica which can be employed as cement substituting material [22][23][24][25] because of its pozzolanic property, and thus environmental pollution can be minimized to some extent [26][27][28][29]. Various research investigations were carried out on concrete blended with 0%-20% of RHA as cementitious material 10%-15% of RHA provides the highest compressive strength of concrete [30]. As size of RHA particle is finer than cement particle, it can improve concrete performance, and it is used as binding material along with cement; therefore, it plays a major role to increase the intertransition zone of concrete [31,32]. It also makes concrete dense by working as filler material [33].
According to facts and figures given in 2015 by the Food and Agricultural Organization of the United Nations, wheat production per annum was determined as 734.5 million tons [34]. Wheat straw is acquired after harvesting the wheat crop on removal of stubbles, and with production of each kg of grain, about 1.3 to 1.5 kg of wheat straw is acquired on average [35]. Worldwide, the annual production of wheat is around 534 million tons, and hence a large quantity of wheat straw is dumped or burned in open space generating environmental pollution. To accommodate such situations, various strategies have been recommended over the burning of wheat straw such as being utilized as fuel for energy production [36], being feed for livestock [37], transforming it as fertilizer, and then utilizing it into the soil for crop productions [38]. But every alternative has few drawbacks [39].
is research recommends incineration as an alternative to disposing wheat straw, while incineration is a process of waste burning in the controlled atmosphere which has the most important advantage that this process lessens the amount of waste by 90% and landfill sites required for dumping waste [40,41]. erefore, this process is much feasible in urbanized countries like Japan where land available for dumping wastes is too expensive and there is exceptional demand for land. With the incineration process, many developed countries are generating energy [42] which is utilized to further generate electricity [40]. e resulting wheat straw ash possesses pozzolanic property, and thus it is consumed as cement substituting material in construction activities; besides, it releases trivial amount of carbon dioxide in the atmosphere [43]. Moreover, researchers observed that concrete strength increased with the introduction of pozzolanic materials, but due to the low hydration activity of pozzolanic materials such as WSA, strength development in concrete is very slow.
Furthermore, most of the investigations were carried out on concrete blended with WSA and RHA as cementitious material individually, but there is no research work that explored the workability, water absorption, density, compressive strength, splitting tensile strength, flexural strength, and drying shrinkage of concrete incorporating RHA and WSA as ternary cementitious material (TCM) in the mixture. In addition, both RHA and WSA were combined owing to their complementary chemical composition. For instance, RHA has silica as dominant oxide, while WSA has good filling effect in cementitious mixture, but it is not too strong in silica. us, combining these TCMs helps in providing pozzolanic effect and filling effect in the developed mixtures. Moreover, this research addresses sustainability issue, and its main focus is to explore the use of RHA and WHA as alternative materials for concrete production, since they are dominant materials in our region.
us, the research is focused on the beneficial utilization of the materials for construction application. erefore, this article summarizes the effect of RHA and WSA as TCM on the fresh property, physical properties, mechanical properties, and drying shrinkage of concrete.

Material.
e rice husk was obtained from an agricultural field near Hyderabad, Sindh, and then it was burnt under an uncontrolled temperature arrangement for five hours to convert into rice husk ash (RHA). After obtaining ash, it was passed from sieve #300 for excluding outsized particles; after that, sieved ash was used in place of cement within mixture. en, the wheat straw was obtained, and it was burnt under an uncontrolled temperature arrangement for five hours to convert it into wheat straw ash (WSA). After obtaining ash, it was passed from the #300 sieve for eliminating unwanted materials and then the sieved ash was used as cementitious materials in the mixture. Moreover, the Portland cement (PC) was collected from the local market, and it was employed as binder in mixture. Composition of oxides of PC, WSA, and RHA is presented in Table 1. Furthermore, stones used were crushed for this research work as coarse aggregates (CAs) which possess a size of 20 mm, hill sand was used for experimental study, and fine aggregates used were passed by #4 sieve. According to ASTM 2 Advances in Civil Engineering C136 [45], aggregate sieve analysis is calculated. e specific gravity of coarse aggregates (CAs) and fine aggregates (FAs) is calculated according to ASTM C127-93 [46] and ASTM C128-93 [47] correspondingly. e ASTM C29-97 [48] code of conduct is used to determine aggregates' bulk density, while the ASTM C127-93 [46] and ASTM C128-93 [47] codes of practice are used to determine water absorption of coarse and fine aggregates, respectively. ese aggregates were obtained from Hyderabad, Sindh, and their properties are shown in Table 2, and the sieve analysis curve for coarse and fine aggregates is summarized in Figures 1 and 2. Moreover, water suitable for drinking was used for mixing as well as curing of concrete.

Mix Proportions.
e mixing process in this investigation followed the standard practices used in conventional concrete mixing, and all of the mixing was done manually. For raw material preparation, PC, aggregates, RHA, WSA, and water were all weighed. e dry mix was first completed by manually mixing PC, aggregates, WSA, and RHA in a mixer until they were uniformly mixed. After that, water was added to the dry mix. e mix was mixed until the wet mixture was changed to a homogenous mixture, and then the workability of fresh concrete was checked immediately. After checking the workability, the fresh mixture of concrete was poured into moulds and left for 24 hours for achieving desired shape and was kept in curing until testing. ese concrete specimens were used for physical (water absorption and density) and hardened properties (compressive strength, splitting tensile strength, flexural strength, and drying shrinkage) of concrete blended with TCM0 (0% WSA+ 0% RHA), TCM5 (2.5%WSA+ 2.5%RHA), TCM10 (5% WSA+ 5% RHA), TCM15 (7.5% WSA+ 7.5% RHA), and TCM20 (10% WSA+ 10% RHA) in the mixture. In this regard, a total of 240 concrete samples (cylinders, cubes, and beams) were equipped with 1 : 2 : 4 mix proportions at 0.50 water-cement ratio and cured at 7 and 28 days, respectively. e mix proportions are mentioned in Table 3 Figure 3.

Slump Test.
e test performed to measure fresh concrete consistency by addition of WSA and RHA as ternary cementitious material (TCM) is indicated in Figure 4. e optimum value of slump recorded on control mix was 62 mm, and the minimum slump value noted was 24 mm at 10% WSA along with 10% of RHA as TCM in the mixture. It can be perceived that the slump of green concrete is dropped with the addition of WSA and RHA together in a mixture.
is drop in slump is due to the high specific surface area of RHA and WSA particles than that of PC as shown in Table 1 which absorb more water as compared to PC while the percentages of RHA and WSA increase in the concrete mixture. Moreover, the 20-24 mm slump is small for practical application. erefore, the study suggests the use of plasticizer for improving the workability of the mixture. is research work is linked with Al-Akhras and Abu-Alfoul [56] where slump declined with the increase in dosages of WSA

Density of Concrete.
Concrete density using different percentages of WSA and RHA as TCM determined after 28 curing days is presented in Figure 5. However, density of concrete recorded by 2374, 2342, 2300, and 2288 kg per m 3 at 5% (2.5% WSA+2.5%RHA), 10% (5% WSA+5%RHA), 15% (7.5% WSA+7.5%RHA), and 20% (10% WSA+10%RHA) is lower when compared with control mix. It can be seen that the density of concrete has plummeted as the dosages of WSA and RHA rise in the mixture. is reduction in density is due to the fact that the specific gravity of WSA (2.21) and RHA (2.23) is lower than that of cement (3.13). is statement was specified in [59] where the density of concrete declined with the increase of dosages of millet husk ash in the mixture at 28 curing days. is comparable investigation has been performed by Raza et al. [60].

Water Absorption of Concrete.
e test performed on hardened concrete mixture by incorporating WSA and RHA as ternary cementitious material at 28 curing days is    Advances in Civil Engineering indicated in Figure 6. e maximum water absorption is noted as 3.75% at control mix, and the minimum value is noted as 1.88% at 10% WSA and 10% RHA as TCM in concrete mix at 28 days. e outcome is that the water absorption of hardened concrete is reduced with the addition of WSA and RHA together in the concrete mixture. is decline in water absorption is due to the size or finest particles of RHA and WSA compared to PC as shown in Table 1 which seals the remaining micropores left by other constituents of concrete while the percentages of RHA and WSA increase in the concrete mixture. is investigation work is related to Auta et al.'s study [61] where water absorption declined with the increase in incorporation of millet husk ash in concrete. is comparable investigation has been performed by Dharani et al. [62] and Raza et al. [60].

Compressive Strength of Concrete.
e test performed on cubical specimen made with concrete by addition of WSA and RHA as TCM is indicated in Figure 7.  WSA along with 10% of RHA as BCM in concrete after 7 and 28 days consistently. e test results pointed out increment in hardened concrete strength while using up to 5% of WSA and 5% of RHA together because of fineness of RHA and WSA particles that occupied micropores left by other concrete ingredients while using concrete up to 5% of WSA and 5% of RHA together. Anwar et al. [63] corroborated this report following their assessment of the effect of ternary binder blends on the concrete microstructure. is starts declining owing to dilution influence of WSA and RHA on cement which reduces the pozzolanic reactions among the concrete ingredients. e result showed that a ternary blend of cementitious materials exhibits superior performance of concrete. In related study, the use of a combination of high calcium fly ash (HCFA), palm oil fuel ash (POFA), and rice husk ash (RHA) proved highly effective for cementitious application in soil [64]. Also, a similar result was obtained in [65] where strength improved by using 7.5% of fly ash along with 7.5% of silica fume in the mixture after 7 and 28 days, respectively. In [66], the strength of concrete is improved while using 5% RHA and 5% of SCBA in the mix after 7, 28, 56, and 90 days, respectively.

Splitting Tensile Strength.
e test performed on cylinder specimen made of concrete with the addition of WSA and RHA as TCM is indicated in Figure 8. e highest splitting tensile strength calculated is 2.74 MPa and 3.52 MPa at 5% of WSA along with 5% of RHA, and the smallest strength is recorded as 2.05 MPa and 2.92 MPa while utilizing 10% of WSA along with 10% of RHA as TCM in concrete after 7 and 28 days consistently. e test results pointed out increment in hardened concrete strength by using up to 5% of WSA and 5% of RHA together because of their larger specific surface areas  Advances in Civil Engineering as compared to cement, and with the further addition of WSA and RHA in the mixture, it starts declining which may be associated with low calcium hydroxide in mixture as dilution impact of WSA and RHA. A similar aspect was attained in [67] where strength improved by using 10-15% of RHA and oil palm shell ash in the mixture after 28 days, respectively. An analogous trend was shown by Kumar et al. [68] and Umamaheswari and Vigneshkumar [69]. A correlation was found between splitting tensile strength and compressive strength, as shown in Figure 9. At all ages, there is a good relationship between splitting tensile strength and compressive strength, as shown in Figure 9. e equations in Figure 9 can be used to estimate compressive strength or splitting tensile strength when one of these properties is known.

Flexural Strength of Concrete.
is test is performed on the beam specimens made of concrete with the addition of WSA and RHA as TCM as indicated in Figure 10. e highest flexural strength calculated is 4.05 MPa and 4.86 MPa at 10% of TCM (5% of WSA along with 5% of RHA), and the smallest strength is recorded as 3.40 MPa and 4.0 MPa while utilizing 20% of TCM (10% of WSA along with 10% of RHA) in concrete after 7 and 28 days consistently. e test results showed increased flexural strength by using up to 10% of TCM (5% of WSA and 5% of RHA), while with the further introduction of TCM in mixture, the strength tends to decrease. is observation may be the effect of TCM dilution on PC, which leads to the fact that the transition zone of the interface is not improved and,   Advances in Civil Engineering therefore, affects the long-term flexural strength, and with the further addition of WSA and RHA in the mixture, it starts declining which may be associated with low calcium hydroxide in mixture owing to dilution effect of WSA and RHA. A similar trend was presented in [68] where strength improved by using 10% of coconut shell ash and egg shell powder in the mixture after 28 days. A similar type of trend was presented by Umamaheswari and Vigneshkumar [69] and Mo et al. [70]. Figure 11 shows the relationship between flexural strength and compressive strength of concrete mixture. ere is a strong linear relationship between these features, as can be seen in the graph. e flexural and compressive strengths, on the other hand, have a more linear relationship. Nonetheless, the two formulations in Figure 11 will be helpful in determining the properties of TCMcontaining concrete mixtures at 28 days.

Drying Shrinkage.
In order to control cracks, it is essential to understand the features of concrete shrinkage and its beginning point in the construction of structures. Figure 12 describes outcomes of RHA and WSA as ternary cementitious material on the drying shrinkage of the mixture at 5, 10, 15, 20, 30, 60, and 90 days, respectively. e outcome of the research study is that the drying shrinkage of concrete is decreased with rising content of RHA and WSA as TCM in concrete. is decrement in drying shrinkage of PC pastes may be due to few causes like PC dilution by RHA and WSA, a lesser quantity of PC generating a smaller amount of shrinkage, the pozzolanic reaction of RHA and WSA with calcium hydrates (CH) produced by PC, and increase in capillary tension [70][71][72]. is observation is in agreement with [73][74][75][76][77]

Advances in Civil Engineering
concrete. is decrease in drying shrinkage can be due to the RHA and WSA's finer particles, which act as a filler and plug the pores, slowing the rate of shrinkage in the concrete. On the other hand, it may be due to the size of pore and grain size improvement procedures which build up the mechanical interlocking in the transition zone. erefore, when shrinkage is a concern, the utilization of RHA and WSA can be a part of the strategy to mitigate its effect. According to Lai et al. [78], shrinkage decreases as the amount of cement replacement material (such as ash) increases. e reduction in shrinkage is due to the concrete's wet packing density. A similar kind of research work was conducted in [79] where the drying shrinkage of concrete lowered due to replacement of PC with fly ash, WSA, and maize cob ash as a tertiary cementitious material in concrete.

Conclusions
is study determined the mechanical properties of concrete incorporating rice husk ash and wheat straw ash as a ternary cementitious material. e categories of properties explored covered the workability and hardened concrete properties. e following conclusions were drawn from the study: materials; thus, the control mix had a slump of 62 mm, and the lowest slump was 24 mm for 10% of WSA and 10% of RHA. Similarly, the density and water absorption measured in the control mix exceeded the modified concrete samples after the 28-day curing regime. (ii) Generally, for all mixes, the compressive strength, splitting tensile strength, and flexural strength characteristics increased with increasing curing regimes. e study showed that the strength development in the modified concrete exceeded that of the control mix. A mix with 10% supplementary cementitious material yielded the highest strength. However, the strength slightly drops as SCM content goes beyond 10%. (iii) e drying shrinkage of the concrete samples reduced as the replacement of PC with RHA and WSA increased. Overall, a concrete mix having 5% RHA and 5% WSA contents exhibited the best performance in terms of fresh and hardened state properties.
Data Availability e datasets generated during the current study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflict of interest.