Optimizing High Performance Self Compacting Concrete

This paper’s objectives are to learn the effect of glass powder, silica fume, Polycarboxylate Ether, and gravel to optimizing composition of each factor in making High Performance SCC. Taguchi method is proposed in this paper as best solution to minimize specimen variable which is more than 80 variations. Taguchi data analysis method is applied to provide composition, optimizing, and the effect of contributing materials for nine variable of specimens. Concrete’s workability was analyzed using Slump flow test, V-funnel test, and L-box test. Compressive and porosity test were performed for the hardened state. With a dimension of 100x200 mm the cylindrical specimens were cast for compressive test with the age of 3, 7, 14, 21, 28 days. Porosity test was conducted at 28 days. It is revealed that silica fume contributes greatly to slump flow and porosity. Coarse aggregate shows the greatest contributing factor to L-box and compressive test. However, all factors show unclear result to V-funnel test.


Introduction
Condensed Silica Fume is now commonly used as a cementitious supplementary material in concrete [1].It improves the strength of concrete and also the durability of concrete [2].Using waste glass powder as supplementary material for cement is quite popular worldwide due to the increased disposal costs and environmental concern.It contains silica based material in amorphous form, and increase the strength of concrete [2][3][4].It was also found promising to be added in Self compacting concrete mixture [5].Previous study showed that using silica fume and glass powder as cement replacement could be used to gradually increase strength of concrete paste [6,7].Self Compacting Concrete is well known for its workability, which can provide many advantages such as lower the rates of human error, doesn't need any compacting activities, can fill through narrow gaps, etc [8][9][10][11][12][13].Using this previous study as reference, High Performance Self Compacting Concrete should be developed to increase the productivity and quality for the construction.It is complicated to optimize the mix design using trial and error, since it is time and energy consuming, therefore using statistic method is helpful to obtain more result with less trial and error, since it is time and energy consuming, therefore using statistic method is helpful to obtain more result with less trial and error.
Fractional factorial designs was known as money and time saver statistical approach.Despite being widely and effectively used, this method become unwieldy in cost and time the number and variables is large, two designs for same experiments may resulting different results, and the interpretation of the experimental result with a large number of factors may be difficult due to lack of clear design and analysis guidelines.Genichi Taguchi of Japan proposed an innovative method by simplified and standardized fractional factorial designs, thus he able to overcome the limitation of fractional factorial designs.[14] This paper discusses about the optimizing and the contributing factors of high performance self compacting concrete using Taguchi's single response method as the data analysis.

Material
Aggregates.The densities of coarse aggregate (±1.2 cm) and fine aggregate are 2.74 g/cm3 and 2.72 g/cm3 respectively.Superplasticizer.There were two kind of superplasticizer used in the mixture to achieve the workability of concrete, which are Polycarboxylate Ether and Polyhydroxy Carbon Salts.Polycarboxylate Ether was used in the controlled factors as shown in Table 1.Polyhydroxy Carbon Salts was used as additional superplaticizer with 0.2% from binders weight.
Binders.Ordinary Portland Cement (OPC) with specific gravity of 3.14 gr/cm3.Silica Fume with specific gravity of 2.105 gr/cm3.Waste ground glass with specific gravity of 2.381 gr/cm3.Ground glass need to be pulverized before applied as cement replacement, after that particle size distribution was conducted.Using glass powder with size in average of 25 μm which its distribution as shown in Fig. 1.

Methods
The composition of binders were determined from previous research [6,7].Using Taguchi analysis method, the factors, levels, degrees of freedom, and orthogonal array need to be determined to generate the mix design [14,15] as shown in Table 1, Table 2, Table 3, and Table 4 respectively.Using glass powder (10%, 15%, 20% from total weight of cement plus glass powder), silica fume (20%, 40%, 60% from total weight of glass powder plus silica fume), Polycarboxylate Ether (0.8%, 1%, 1.2% from binder's weight), and coarse aggregate (45%, 50%, 55% from total volume of aggregate) as the controlled factors.Fresh concretes were tested for slump flow test, V-funnel test, and L-box test [16].After that, the fresh concrete was casted in cylindrical molds with a diameter of 100 and 200 mm high [17].One day after casting, concretes were cured in water (wet curing system) until the age of 3, 7, 14, 21, and 28 days to be tested for compressive strength.One day before compressive test, the rough top surface of concrete was cut to obtain smooth and solid surface.The compressive test is corrected using correction factor, since length of cylinder may be less than initial condition [18,19].Porosity test conducted at the age of 28 days.

Results and discussions
Concrete's test result is shown by Table 5.This result agreed with previous study [5][6][7] that Silica Fume absorb more water than glass powder.Adding more silica fume resulted in fresh concrete more condensed.In addition, adding glass powder shows better workability.It was noted that in R6 and R8 bleeding occurred, which contains higher glass powder.It is proved that adding glass powder cannot reduce bleeding.
V-Funnel.It is found that no factors have significant effect on the V-funnel.Which means that there are other factors or other levels that may have significant effect on V-funnel that were not estimated during the experiments.The optimum condition could not be estimated, however the composition can still be used.Using 40% of silica fume by glass powder weight is recommended.In addition, 10-15% of glass powder is also recommended.Since the density of silica fume is less than glass powder, it influence the performance of fresh state of concrete.Hence, bleeding of concrete can be avoided.

L-
Applying 1% of Polycarboxylate Ether is recommended to achieve better workability.Furthermore, to obtain less porous in concrete, it is recommended to use superplasticizer up to 1.2% because it can produce denser concrete.In consequences, it decrease the strength.
It is proved that controlling the volume of coarse aggregate plays an important role to produce high performance concrete in hardened state.Less coarse aggregate leads to compacted concrete.

Table 1 .
Factors and Level

Table 2 .
Degree of Freedom

Table 4 .
Mix Design