The Effect of Styrofoam Artificial Lightweight Aggregate ( ALWA ) on Compressive Strength of Self Compacting Concrete ( SCC )

Self-compacting concrete (SCC) is a fresh concrete that is able to flow and fill up the formwork by itself without the need of a vibrator to compact it. One of the reasons that causes the damage of a building structure during an earthquake is the heavy weight of its structural members which are from the high density of the material used such concrete material. Lightweight aggregate is one of the solutions to reduce the weight of the structure. Therefore, the SCC using the artificial lightweight aggregate (ALWA) is one of the solutions to reduce the self-weight (dead load) of a structure. This research was conducted to investigate the impact of the use of ALWA in conventional concrete and SCC in terms of its compressive strength and modulus of elasticity. To study the impact of the use of ALWA in SCC, several variation of percentage of ALWA as a substitution to the natural coarse aggregate was examined. The proportions of ALWA as a replacement to the coarse aggregate were 0%, 15%, 50%, and 100%. The test specimens were the cylindrical concrete of 200 mm in height and 100 mm in diameter for both compressive strength and modulus of elasticity tests. The results of the compressive strength test indicated that the higher the percentage of ALWA used in SCC, the lower the compressive strength of the concrete. The addition of ALWA as a substitution to the natural coarse aggregate to conventional concrete and SCC was found optimum at 15% replacement with the compressive strength of conventional concrete and SCC of 21.13 and 28.33 MPa, respectively. Whereas, the modulus of elasticity of the conventional concrete and SCC were found to be 20,843.99 and 23,717.77 MPa, respectively.


Introduction
Concrete is one of the options for structural materials and its use is the most popular in the construction among others [1][2][3].However, its heavy weight brings another issue to the buildings particularly in terms of construction and its vulnerability to earthquake disaster.An earthquake is one of the natural disasters that can cause severe damage to the building structures [4][5][6].The earthquake force received by the building structure is directly proportional to the weight of the corresponding building.Lightweight concrete is used as an alternative to reduce the self-weight of the building structure such that it can mitigate the damage of the building structures due to the severe earthquakes.Therefore, the need of lightweight materials becomes increasingly popular and required urgently for various applications in the modern construction technology for structural members [7,8].This is due to the various advantages that can be obtained from the use of lightweight concrete material, such as smaller density of concrete resulting in lower self-weight of the structural members [9,10].To be categorized as lightweight concrete, its density should be less than 1840 kg/m 3 [11].
Besides, the structural members must still conform the requirements particularly on the compressive and tensile strengths for the lightweight concrete when used for structural purposes.
Lightweight concrete is known for good performance and durability when it was made properly during the mixing process.In the structural applications, the weight of concrete structures is very important because it also forms the total load of the buildings.The self-weight reduction by using the lightweight concrete can significantly reduce the gravity load and further, the mass of seismic inertia, thereby also reducing the size of structural members such as slabs, beams and columns as well as foundation at the end [12][13][14][15].The reduction also affects the use of reinforcement in the design.Less reinforcement is needed due to the lower stresses or internal forces occurred in structural members [16][17][18][19].Lightweight aggregate concrete has better strain capacity, lower thermal expansion coefficient, and better sound isolation characteristics due to the presence of air cavities in the lightweight aggregate [20].
In concrete construction work, especially conventional reinforced concrete construction, one of the most absolute work to do is concrete compaction or vibration.The purpose of compaction is to minimize the air trapped in the fresh concrete to provide the homogeneous concrete.Incomplete compaction on reinforced concrete members can decrease the compressive strength and durability of concrete that can cause the corrosion of the steel reinforcement in concrete.One of the solutions to resolve that issue is to use the self-compacting concrete or self-consolidating concrete (SCC) or also known as the flow concrete.SCC can flow under its own weight so it can fill up the formwork and reach its highest density [7].In addition, the artificial lightweight aggregate (ALWA) was introduced in SCC to produce the selfcompacting lightweight concrete (SCLC).The ALWA used in SCC was the Expanded Polystyrene (EPS) aggregate.It substitutes the natural coarse aggregate by 10%, 15%, 22.5%, and 30% of the total volume of concrete.The results showed that the greater EPS used in SCC, the smaller density as well as the compressive strength of concrete [21].The EPS aggregate is a low density material and it does not absorb the mixing water [22].Concrete with lightweight aggregate is an excellent solution to reduce the self-weight (dead load) of the structures.The application of ALWA in SCC provides several advantages in terms of cost and construction time, since it can eliminate the compaction process and better workability [23].
Based on the styrofoam lightweight aggregate concrete research which has been conducted previously by several researchers, it is known that the compressive strength of concrete decreases with the addition of styrofoam percentage in concrete as a substitution to the natural coarse aggregate.This is due to that the styrofoam is weaker compared to the natural coarse aggregate such as crushed stone [24].Styrofoam grain can be formed into different specific sizes as required and it depends on the temperature during the evaporation process.The higher the temperature, the larger size and the more likely the occurrence of microscopic cracks [25].The styrofoam was dissolved with the acetone solution and then formed into granules such that it resembles the shape of the natural coarse aggregate.After resembling the coarse aggregate then it was coated with the paste.This study was to investigate the use of styrofoam ALWA in SCC and their mechanical properties such as the compressive strength and modulus of elasticity as well as the characteristics of the fresh SCC such as its workability by slump or flow test and the density of using ALWA.

Materials
The hydraulic cement used in this research was the Type I Portland cement or Ordinary Portland Cement (OPC).Coarse aggregate used Artificial Lightweight Aggregate (ALWA) was made from styrofoam material, acetone solution, and mortar.The composition ratio of acetone solution and styrofoam material was 1:1.9.After the ALWA grain was formed, then it was coated by the mortar with the ratio of sand: cement: water: adhesive of 1:1:0.25:0.025.The result of the styrofoam ALWA produced by the process is shown in Figure 1.Crushed stone in this research was also used in SCC as the partial natural coarse aggregate which was partly or completely replaced by the styrofoam ALWA.Fine aggregate used was the natural sand.The superplasticizer was used to improve the workability of the concrete mixture.

Mixture Proportion
The mixture proportion was obtained from the mix design.The calculation depends on the data which was observed in the laboratory work to perform more accurate calculation based on the actual conditions of the constituent materials of concrete such as the density, specific gravity, coarse and fine aggregate sieve analysis or gradation.The various compositions of concrete mixture prepared for comparisons in the study are given in Tables 1 and 2.

Test Methods
In this research, the specimens used for compressive strength and modulus of elasticity tests were the concrete cylinders with the diameter of 100 mm and the height of 200 mm as many.Twelve cylinders of conventional concrete and twelve cylinders of SCC were prepared and they were cured until 28 days of age before the tests.The fresh concrete test for conventional concrete is the slump test, whereas for SCC, it consists of the flow, T500 slump time, V-funnel, and L-box tests.Testing of compressive strength and modulus of elasticity of concrete were performed with the loading rate conforming ASTM C39/C39M-18 [26] using a Universal Testing Machine (UTM).The machine used to measure the compressive strength of concrete as well as the stress and strain values such that the modulus of elasticity of the concrete can be calculated.The load and displacement were measured using the load cell and transducer, respectively.Data logger was used to read the data from the instrument and a computer system used to record the data from the data acquisition.For each composition, i.e. 0%, 15%, 50%, and 100% ALWA replacement, used three cylinder specimens to provide the representative average values.

Slump Flow Dan T500 Slump Time Tests
The objectives of these tests are to measure the flow ability of SCC without any obstacles.T500 slump time is the time required by the viscosity flow of SCC to spread with the diameter of 500 mm.The slump flow and T500 slump time tests conform EFNARC [27].The shape and size of the baseplate used for these tests can be seen in Figure 2.

V-funnel Test
The V-funnel test is to determine the viscosity and filling ability of the SCC.The test is to define the time required by the SCC to flow out from the V-funnel.The test is not suitable when the coarse aggregate size is greater than 20 mm.The V-funnel test conform EFNARC [27].The shape and dimensions of the apparatus for the test is shown in Figure 3.

L-box Test
The L-box test is used to measure the passing ability of SCC through the spaces between bars or obstacles without experiencing segregation or clogging.The test also conforms EFNARC [27].The shape and dimensions of L-box can be seen in Figure 4.

Sieve Segregation Resistance Test
The sieve segregation resistance test is to measure the resistance of SCC against the segregation of coarse aggregate.The sieve segregation resistance test refers to EFNARC [27].The segregated or separated portion of the SCC can be calculated using the following equation: Where: SR = segregated portion (%).
Wps = weight of fresh concrete passing the sieve (gr).
Wp = weight of the sieve (gr).
Wc = weight of the fresh concrete on the sieve (gr).

Testing of Materials
The materials used in this research included the natural coarse and fine aggregates besides the styrofoam ALWA.The test results of the materials, such as sand, crush stone, and the styrofoam ALWA are given in Table 3.All the tests conducted for the fine and coarse aggregates as well as ALWA, namely unit weight (gr/cm³), density (gr/cm³), absorption (%), sieve analysis (fine modulus), materials finer than 75-µm (%), total evaporable moisture (%), abrasion (%), impact, and organic impurities, indicate that all the results satisfy the requirements to be used as concrete materials.For the gradation of sand and crush stone are shown in Figures 5 and 6.In the test, the sand used for SCC was found within zone II (medium category sand).Based on ASTM C136/C136M-14 [28], a good aggregate is an aggregate that falls within a predetermined sieve.From Figure 5, it can be seen that the sand used has met the requirements.The limit of fine modulus value for fine aggregate is 1.5 to 3.8.From the test, it was obtained that the fine modulus values from Tests 1 and 2 were 3.79 and 3.80, respectively.This indicates that the fine modulus has satisfied the requirements.The coarse aggregate complies with the maximum sieve of 20 mm [28].The limit of fineness modulus for the coarse aggregate is between 6.0 and 7.1.From the test results, the fineness modulus for Tests 1 and 2 were found to be 6.62 and 6.50, respectively.Hence, the fineness modulus of the course aggregate has satisfied the requirements.

Testing of Fresh Concrete Slump
The fresh concrete was observed by using the slump test for its workability.The slump test was conducted to obtain the slump value which can be used as a benchmark of the concrete mixture in association with the level of workability.The results of fresh concrete test for each mixture are listed in Tables 4 and 5. Replacement of the natural coarse aggregate with the styrofoam ALWA in the conventional concrete did not improve the workability.This can be seen from the slump test results that was less than that of the conventional concrete without the styrofoam ALWA.While on SCC concrete for slump flow test results can be seen in Table 5.The results of the slump flow tests of specimens SCC0 and SCC15 indicated that the addition of 15% of the styrofoam ALWA can reduce the diameter of slump flow.However, the results of both tests still satisfied the EFNARC [27] where the limit of the allowable slump flow is between 65 and 80 cm.The results of slump flow tests of specimens SCC50 and SCC100 failed to conform the standard due to the segregation occurred between the coarse and fine aggregates.For the results of the T500 slump time of SCC50 and SCC100, both are not eligible since the EFNARC [27] requires the fresh SCC to have the T500 slump time value from 2 to 5 seconds.For more details, results of the slump flow tests of each SCC are shown in Figure 7.The results of the V-funnel, L-box, and Segregation Resistance Tests for fresh SCC of all specimens are listed in Table 6.The results of all these tests refer to the EFNARC [27].From the results of V-funnel test, it was found that the concrete mixture with 0%, 15%, and 50% replacement meet the requirements since the concrete was able to flow through the V funnel and took times of 6 to 12 seconds.While, for the L-box test only 0% and 15% replacement mixtures satisfied the requirements in which the values of H2 /H1 are in between 0.8 and 1 [27].

Density of Concrete
The densities of both conventional concrete and SCC shown in Table 7 are the average densities of six cylinders from each mix design.The relationship between the density of conventional concrete and SCC and the percentage of styrofoam ALWA replacement is shown in the graphical manner in Figure 8.

Figure 8. The relationship between the density of conventional concrete and SCC and the percentage of styrofoam ALWA replacement
From Figure 8, it can be seen that the higher percentage of the styrofoam ALWA used in concrete the lower its density.This was occurred due to the specific gravity of the styrofoam ALWA is smaller when compared to the specific gravity of the natural crush stone, i.e. the specific gravity of the styrofoam ALWA was only 1.190, while the specific gravity of the natural crush stone was about 2.669.According to the ASTM C330/C330M-17 [29], the concrete can be classified into lightweight concrete if its density does not exceed 1840 kg/m 3 .From the results of density measurement shown in Table 6, it can be seen that all the conventional concrete and SCC do not conform the requirement since their densities are above 1840 kg/m 3 .However, the density of conventional concrete with 100% styrofoam ALWA replacement to the natural coarse aggregate can reduce the density of concrete up to 13.21% lower than the conventional concrete without styrofoam ALWA.

Compressive Strength
Testing of compressive strength on conventional concrete were carried out when the concrete was at 28 days of age.The test procedure for compressive strength test is based on the ASTM C39/C39M-18 [26].The results of compressive strength tests on conventional concrete are given in Table 8.From Table 8, it can be seen that the higher the percentage of styrofoam ALWA replacement in concrete, the lower its compressive strength.The optimum styrofoam ALWA replacement to the natural coarse aggregate in concrete was at about 15% which produced the highest compressive strength of 21.13 MPa.
In accordance with the ACI 318M-14 [11], the minimum compressive strength required for seismic-resistant concrete structures is 21 MPa, whereas for the structural concrete is 17 MPa.From the results of the compressive strength tests of the conventional concrete, it can be found the optimum percentages of styrofoam ALWA that conform both minimum values of concrete compressive strengths (i.e.21 and 17 MPa) for seismic-resistant concrete structures and structural concrete, respectively [30].The correlation between the compressive strength of conventional concrete and the percentage of styrofoam ALWA replacement is shown in Figure 9.The results of the compressive strength tests of conventional concrete with styrofoam ALWA were plotted to form a curve shown in Figure 9.It can be seen that the 21 MPa compressive strength can be achieved when 14% styrofoam ALWA was used as a replacement to the natural coarse aggregate.To achieve the 17 MPa compressive strength of concrete, higher percentage of styrofoam ALWA as much as 92% can be applied.
Testing of compressive strength on self-compacting concrete (SCC) were carried out when the concrete was at 28 days of age.The test procedure for compressive strength test is based on the ASTM C39/C39M-18 [26].The results of compressive strength tests on SCC are listed in Table 9.The crack and failure patterns of conventional concrete for specimens C0, C15, C50, and C100 are shown in Figure 10.From Figure 10, it can be seen the crack and failure patterns of specimens C0, C15, and C100 can be categorized as shear type, whereas specimen C50 is in the category of cone-shaped and shear type pattern.The four test specimens are considered conforming the requirements of ASTM C39/C39M-18 [26].For the results of the compressive strength test on SCC can be seen in Table 9.
Based on Table 9, it can be seen that the increase of styrofoam ALWA replacement resulting to the decrease of compressive strength of concrete.The highest compressive strength of SCC with styrofoam ALWA was attained at about 15% replacement with the corresponding compressive strength value of 28.33 MPa.
The relationship between the compressive strength of SCC and the percentage of styrofoam ALWA replacement is given in Figure 11.The optimum percentage of styrofoam ALWA replacement to the natural coarse aggregate for SCC can also be found from the correlation generated in Figure 11 to achieve the minimum compressive strength requirements for both seismic-resistant concrete structures (21 MPa) and structural concrete (17 MPa) [31].From Figure 11, it can be found that the percentage of styrofoam ALWA replacement to achieve 21-MPa concrete is about 55%, whereas to achieve the compressive strength requirement to satisfy the structural concrete of 17 MPa [32,33], 100% styrofoam ALWA can be used to replace all the natural coarse aggregate.The crack and failure patterns of SCC for specimens SCC0, SCC15, SCC50, and SCC100 can be seen in Figure 12.

Specimen SCC0
Specimen SCC15 Specimen SCC50 Specimen SCC100 Figure 12.Failure and crack patterns of SCC From Figure 12, it is shown that the crack and failure patterns of specimens SCC0 and SCC15 can be classified as shear-type pattern whereas for specimens SCC50 and SCC100 can be defined as the columnar-type pattern.The crack and failure patterns of allfour specimens satisfied the requirements as per ASTM C39/C39M-18 [26].

Modulus of Elasticity of Concrete
The test results of modulus of elasticity of conventional concrete and SCC are listed in Tables 10 and 11.According to the ACI 318M-14 [11], the modulus of elasticity of concrete can be computed by dividing the stress value (0.45fc) with the strain corresponding to 45% of its peak stress.From Tables 10 and 11, it can be seen that the higher percentage of styrofoam ALWA used in concrete the smaller the strain value.The correlation between the modulus of elasticity and the percentage of styrofoam ALWA replacement is presented in Figure 13.From Figure 13, it can be seen that the more styrofoam ALWA replacement in both conventional concrete and SCC, the smaller the modulus of elasticity of concrete.The modulus of elasticity of SCC is higher than the modulus of elasticity of conventional concrete.

Conclusions
From the results of study, the followings conclusions can be drawn:  The compressive strengths of both conventional concrete and SCC decrease with the increase of the amount of styrofoam ALWA replacement.The higher the percentage of styrofoam ALWA replacement, the lower the compressive strength.The replacement to the natural coarse aggregate in both conventional concrete and SCC resulted the highest compressive strengths at about 15% with the compressive strengths of conventional concrete and SCC of about 21.13 and 28.33 MPa, respectively.
 The more styrofoam ALWA replacement, the smaller the modulus of elasticity of concrete.The modulus of elasticity of SCC is greater than that of the conventional concrete.
 The higher amount of ALWA used in self-compacting concrete (SCC), the lower workability level can be reached.

Figure 2 .
Figure 2. Baseplate for slump flow test

Figure 4 .
Figure 4. L-box To calculate the passing ability, the following equation can be used: PA = H2/H1 (1) Where: PA = passing ability.H1 = height of fresh concrete in box I (mm).H2 = height of fresh concrete in box II (mm).

Figure 6 .
Figure 6.Gradation of coarse aggregate with maximum size of 20 mm

Figure 7 .
Figure 7. Results of slump flow tests of SCC

Figure 9 .
Figure 9.The relationship between the compressive strength of conventional concrete and the percentage of styrofoam ALWA replacement

Figure 10 .
Figure 10.Failure and crack patterns of conventional concrete

Figure 11 .
Figure 11.The relationship between the compressive strength of SCC and the percentage of styrofoam ALWA replacement

Figure 13 .
Figure 13.The relationship between the modulus of elasticity of concrete and the percentage of styrofoam ALWA replacement in both conventional concrete and SCC