Computational and experimental analysis of reinforced aerated concrete beam concrete containing rice husk ash

Aerated concrete, which is manufactured from binding material, sand, foaming agent and water, is currently being utilized in the construction industry because of its lightweight and durability. The binding material, cement, along with other materials used in the concrete produces huge carbon footprints during its fabrication. The utilization of natural aggregates name as coarse aggregates depletes the natural resources of the country. Therefore, huge amounts of agricultural wastes have led scholars to investigate the effectiveness of replacing conventional materials used in concrete with agricultural wastes. In the current study, rice husk ash (RHA) was used as supplementary cementing material, thereby reducing the amount of cement used in aerated concrete (AC) mixture will reduce carbon footprints. The experimental and numerical analysis were conducted to investigate structural behavior of reinforced RACB beams subjected to flexural load. Parametric study on structural performance of RACB beam under flexure were conducted using finite element analysis (FEA). From the experiment and FEA. Results from the parametric study showed that RAC-10%RHA-B with higher depth structurally performed better compared to RACB under flexure with greater load carrying capacity, lesser maximum deflection, and less cracks developing in the tension area.


Introduction
At present, construction industry mostly utilizes concrete to manufacture structural members.
Concrete serves great application purposes in construction industry such as, construction of skyscrapers, bridges, water reservoirs, highways and buildings [1][2][3]. The rapid development of construction industry raises the demand for concrete due to its high strength, durability, on-site molding ability, and better economy in comparison with other building materials [4][5].
Researchers have investigated various kinds of concrete in the past such as, self-compacting concrete, conventional concrete and foamed or aerated concrete. Aerated concrete has a dry density of 300 to 1800 kg/m3, which is 85% lighter than the conventional concrete and falls under the category of Lightweight concrete [6][7]. To reduce the density of concrete, air-voids are introduced by utilizing a foaming agent during concrete manufacture [8]. Aerated concrete is primarily used in the construction of non-structural elements to reduce structural loads [9]. Aerated concrete is manufactured from binding material, foaming agent and sand. Binding material such as cement is greatly used in all kinds of concrete to bind all other constituent materials together to give high strength and hardness. Besides that, the manufacturing of cement creates huge number of environmental problems [10][11]. Cement industry is the source for the release of 10% of the total Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 22 July 2020 doi:10.20944/preprints202007.0510.v1 global carbon dioxide (CO2) emissions. CO2 emissions are highly detrimental for the ozone layer and leads to global warming and climate changes [12][13]. To over this problem great number of researchers are working to introduce the new innovative binding material.
Meanwhile, agricultural solid waste created from residential area, commercial business and institutions is increasing daily. Nowadays 1.3 billion tons per annum global municipal solid waste is produced due to rise in population and enhancement in standard of living, approximately 1.2 kg/capita/day municipal waste is produced, but it increases to 1.42 kg/capita/day in 2020 [14]. One of the attractive solutions to overcome this issue is to recycle the agricultural waste and utilize it as binding material or admixtures to enhance the mechanical properties of concrete. Rice husk ash, Sugar cane bagasse ash, egg shell ash and banana skin powder could be used as partial replacement of cementing material [15].
Experimental analysis of structural member is time, energy and material consuming due to that in this research, reinforced aerated concrete beam model containing RHA was analysed by FEA software package name as ABAQUS explicit under flexural load because it requires less disk space and memory than Abaqus/Standard for the same simulation. For problems in which the computational cost of the two programs may be comparable, the substantial disk space and memory savings of Abaqus/Explicit make it attractive. Subsequent parametric study by changing shear span over depth ratio was conducted and the outcomes from FEA were validated with the experimental and literature studies.

Materials and Methods
The experimental analysis of RAC beam contains the following steps: Specify the beam dimensions, fabrication, and casting, curing and testing under four-point loading condition.

RAC-B specifications
The aim of this study is to investigate the structural performance of RAC-B interms of load deflection, ultimate load and cracking pattern. RAC-B was casted by using 0% and 10% RHA as cement replacement.
RAC-B having 1600 mm total length and rectangular cross sectional width of 100 mm and a depth of 200 mm were used in this research.
Formwork for RAC-B was prepared by using 10 mm thick plywood sheet. The fine aggregate (sand) was properly dried to avoid any influence on water binder ratio. The RHA used in this study was sieved from 45 micron meter because according to ASTM ---90% cement must be sieved from 45 micro meter. The main reinforcement and stirrups were cut into the design lengths as shown in Figure   1.

Testing of RAC-RHA-B
The entire test protocol for the RAC-RHA-B beams can be characterized as follows: • Instrumentation • Procedure • Measurement.

Instrumentation
Beams were instrumented to sufficiently record their response behavior under flexural loads as shown in Figure 2. The instruments and equipment that were adopted in this study were:  After the installation of instruments, load was constantly applied at the mid-section of the beam and transferred load to beam by load spreader by using manually controlled hydraulic jack with a loading rate of 5 kN/min. The flexural load during the beam testing was recorded by the load cell. A data logger was combined to the load cell to record the applied loading and the corresponding deflections until the beam reached the ultimate failure strength.

Measurement
Deflection of the beam was noted by using three linear variable differential transducer (LVDTs) with a gauge length of 120 mm. LVDTs were installed at three different locations, namely, at the mid-span and under the point loading of beam. The base of LVDTs were linked to the steel hooks which were placed at the vertical portion of the beam as the load applied the beam deflect so deflection were recorded as shown in Figure 2 . The LVDTs were joint to the data logger to get the deflection data.
In this way, the attached data logger was developed initial readings for deflection. The results for deflection of the beam at each incremental load were recorded continuously during the test.

Finite element analysis of RAC-RHA-B
The three dimensional-nonlinear finite element beam models were modelled by FEA computer based application Abaqus to analyse the performance of beams under flexural loading.
RAC-B and RAC-10%RHA-B were analysed separately, the part of Abaqus module by adopting different kinds of element based on the suitability of each element. The element used for each part are arranged in Table 1 and Table 2, the element type selected for each part are created on the appropriateness and competence of the element type. The modelling procedure for RAC-RHA-B including discretized geometry, element section properties, material data, loading and boundary conditions, analysis types and output are described in next sections. The RAC-RHA-B model was initially established with geometric discretization of each part.
The steel reinforcement was simulated using three dimensional 2-node elements. The concrete damage plasticity of RAC-B and RAC-10%RHA-B which were extracted from the experimental outcomes are presented in Table 3. The dilatation angle, eccentricity, initial biaxial/ uniaxial ratio, viscosity were taken from Rahman et al. (2019) [16].

Convergence study
The quasi-static analysis method was further method with different element extents as shown in Tables 4 to demonstrate mesh sensitivity. Similar material characteristics were used for all mesh sizes.
Results of the FEA analysis using different mesh density for RAC-B (control sample) are presented in Table 5. Figure  The difference in element number was due to size difference of RAC-RHA-B.

Boundary conditions
The point load was applied at the top surface of the beams and simply supported boundary conditions were provided at the bottom surface of the beam. After the RAC-RHA-B model was assembled, the discrete modelled section was connected appropriately to each other. Embedded approach was implemented to make appropriate interaction between aerated concrete and steel reinforcement as presented in Figure 3. Finally, the convergence of RAC-RHA-B was observed with mesh sensitivity analysis by changing the mesh density to get the final mesh size for RAC-RHA-B. The critical outcomes parameters from the FEA were validated with the experimental results.

Results and discussions
The outcomes such as ultimate load, cracking pattern and load deflection profile of RAC-RHA-B from ABAQUS simulation were extracted from post processing and validated with the experimental results.

Ultimate load
The ultimate load, maximum load carried by the beam before failure, obtained from experiment and FEA are shown in Table 5. The results presented in Table 5 [19], analysed the structural behaviour of reinforced concrete beam by experimental work and FEA.
The outcomes demonstrated that the difference between experimental and FEA outcomes were 10% to 15%.

Cracking profile of RAC-RHA-B
The cracking pattern of all RAC-RHA beams from FEA are shown in The results showed that first crack appeared at the bottom of the beam close to the centre of the span.
The cracks appeared at the tension zone and moved towards the compression zone as load increased.
The outcomes of cracking pattern of RAC-RHA beams from FEA were found to have similar trends as obtained from the experimental work performed for this study and the previous researches.   Table 6 shows the maximum deflection of all RAC-RHA beams as documented from experiments and FEA. RAC-B (control beam) recorded highest maximum deflection value while RAC-10%RHA-B recorded the least deflection value, in both experiments and FEA. From Table 6, it is seen that the maximum deflection obtained from FEA was slightly lesser then the maximum deflection obtained from the experimental results. The percentage difference between FEA and experimental results of maximum deflection are in the range of 5% to 7.5%. This is in good agreement with the results obtained from previous researches conducted by Charan [24]. In these studies, the RCC beams containing fibres were analysed by experiment and FEA. The results demonstrated that the deflection obtained from the FEA were 5% to 15 % less than the experimental analysis.

Preprints
Load-deflection graphs of RAC -B and RAC-10%RHA-B beams are presented in Figure 5, and Figure 6, respectively. These graphs show similar load-deflection profiles from experiments and FEA.  The parametric study was conducted to investigate the effect of beam height on failure modes and load deflection profiles of RAC-10%RHA-B. As the height of the beam greatly influences its structural performance, therefore, it is pertinent to investigate its influence on failure modes and crack patterns.
For this purpose, three different beams of depth 300mm, 400mm and 500mm were investigated.
The impact of different heights on ultimate load, load-deflection pattern and crack profile were analysed. Table 7 demonstrates the structural behaviour of beams with various heights in terms of ultimate load and maximum deflection while all other factors such as, the overall length, width and material characteristics of beam were kept constant.
The results in Table 7 show that the height of beam greatly influences beam strength, and the   Conflicts of Interest: All above mentioned authors declare that there is no conflict of interest.