The effect of crystalline technology on concrete as coating to improve its durability

This research delves into the effects of incorporating Crystalline Additives (CAs) in concrete, specifically exploring alterations in compressive strength, water penetration resistance, and chemical durability when subjected to corrosive solutions, including H2SO4 and HCl. The investigation encompasses four concrete compositions: Standard Concrete, Concrete with Single Layer Crystalline Coating, Concrete with Double Layer Crystalline Coating, and Concrete featuring Type V Cement. Results indicate that the application of Crystalline coating contributes to notable enhancements in the average compressive strength, albeit falling short of the peak strength achieved with Type V cement. Notably, exposure to a 5% H2SO4 solution triggers more pronounced deterioration compared to exposure to 5% HCl, leading to discernible reductions in both weight and compressive strength. Despite Crystalline coating’s beneficial impact on compressive strength, it remains outperformed by the application of Type V Cement, as evidenced by superior average compressive strength values. Conversely, the efficacy of Crystalline coating in countering water penetration remains inconclusive, as evidenced by the water penetration test outcomes. This ambiguity underscores the necessity for further research to ascertain the true extent of Crystalline coating’s influence on water resistance.


Introduction
Construction development in this era has developed very rapidly, such as the construction of buildings, irrigation, roads, bridges, and so on.Concrete is present as one of the choices of structural materials in every construction.According to SNI 2847:2019, concrete is formed from coarse aggregate, fine aggregate, Portland cement, and/or without additives [1].The surrounding environment is one of the factors that can affect construction development.One example is the construction of construction in direct contact with sea water.Sea salt will enter the concrete and fill the cavities in the concrete.So that the initially planned concrete compressive strength will not be achieved because the chemical compounds contained in seawater will highlight the concrete until it is brittle [2].Concrete in direct contact with seawater should use a mixture with Type V cement.However, Type V cement is difficult to find in general building material stores [3].
In Indonesia, additives are widely used.The benefits of adding additives need to be confirmed by using the same aggregates and cement as the materials used in the field.Additives, which are chemicals, must meet the requirements listed in ASTM C494 (Standard Specification for Chemical Admixture for Concrete) [4] [5].Crystalline is one of the additives that can make concrete resistant to water or waterproofing admixture.Crystalline is generally used as protection of the bottom of the building against water and moisture.The waterproofing effect occurs in concrete when various reactions of chemical components contained in the crystalline solution combine with the concrete matrix.The working process occurs when the porous concrete has acquired sufficient moisture.Therefore, sufficient moisture is very important.Because if it is not enough, the crystalline will not actively work [6].

Additive Crystalline
Crystalline is one of the additives that make concrete resistant to water or waterproofing admixture.It works by reacting with cement hydration to prevent water and other corrosive liquids from entering the concrete.Crystalline will form crystals to fill the pores in the concrete and then become a permanent part of the concrete matrix.So as to provide protection to the concrete structure.This additive can be applied to coating concrete surfaces or by mixing directly into the concrete mixture [6].In this research, the type of concrete with One Layer Coating Crystalline, while the concrete with Two Layer Coating Crystalline.

Portland Cement Type V
Type V cement is a type of Portland cement used for high sulphate resistance.According to ASTM C150, Type V cement is limited to a C3A percentage with a maximum value of 5% and a C4AF+2(C3A) percentage that has a maximum value of 25%.When compared to other types of Portland cement, Type II Cement has a maximum percentage of 8% C3A, Type III Cement has a maximum percentage of 15% C3A, and Type IV Cement has a maximum percentage of 35% C3S, then a minimum percentage of 40% C2S, and a maximum percentage of 7% C3A [7][8].Limiting the percentage of C3A and C4AF in Type V cement is done to reduce sulphate attack that occurs internally.This also makes C2S and C3S compounds the dominant compounds, hence the silicate content of Type V Cement is high.Therefore, Type V cement is strong enough.[9]

Slump Test
The concrete slump test is conducted to observe the homogeneity and workability of fresh concrete mix with a certain viscosity.In its implementation in the field, the concrete slump test has a maximum and minimum height limit depending on the needs of the construction type.The concrete slump test is carried out with slump tools, namely piercing rods and Abrams cones [10].
In practice in the field, the concrete slump test has a maximum and minimum height limit depending on the needs of the type of construction which is according to SNI 7656:2012 [11].

Compressive Strength Test
Test the compressive strength of concrete with cylindrical test objects, the compressive strength of concrete is the amount of load per unit area, which can cause the concrete test sample to crumble when loaded by a compressive force with a certain value using a press machine [12].

Water Penetration Test
According to BS EN 12390-8:2009, the water penetration test is the pressure of water applied to a hardened concrete sample.The concrete sample is then split and the depth of penetration measured.The concrete sample used must be in the form of a cube, cylinder, or prism with the dimensions used being a minimum of 150 mm [13].The water penetration test is the ability of concrete to drain through the pores in it.The water penetration test is expressed in the water penetration coefficient in units of cm/s by determining the measurement of the level of water flow through the concrete.The greater the water penetration coefficient, the easier it is for water to pass through the concrete.While the smaller the water penetration coefficient, the concrete will be difficult to pass through water so that the strength of the concrete is higher [14].
The permeability value of concrete is the main index for assessing the durability of concrete.For a material with porosity such as concrete, water penetration will depend on the characteristics and porosity of the cement.If the cement grains used are coarser, the porosity level will be higher.[15]

Slump Test Results
Slump testing of concrete samples was carried out before the concrete mixture was put into the mold to determine the slump value of the concrete mixture.Slump testing is done every time the mixing process is carried out.

Figure 1 Diagram of Concrete Slump Test Results
Based on the slump test results as shown in Figure 1, there is an increase in the slump test value of concrete with Type V Cement compared to other types of concrete.Concrete with Type V Cement has a slump value of 120 mm.Normal Concrete, Concrete with One Layer Coating, and Concrete with Two Layer Coating had a slump value of 100 mm.
By using Type V cement in Concrete with Type V Cement, the slump value is high so that the workability of the concrete mix is easier in the process.Therefore, Normal Concrete, Concrete with One Layer Coating, and Concrete with Two Layer Coating have no better workability than Concrete with Type V Cement.

Compressive Strength Test Results
The compressive strength test of concrete samples is carried out to determine the compressive strength value of each concrete sample in the form of a cylinder with a size of 150 × 300 mm.This test was carried out after curing for 28 days as well as some concrete that had been coated using Crystalline.The application of Crystalline coating on concrete samples makes the concrete have a higher average compressive strength test value than normal concrete.In addition, the use of Type V cement in Concrete with Type V Cement is effective in compressive strength testing than other types of concrete because it has the highest average compressive strength test value.

Water Penetration Test Results
Water penetration testing of concrete samples is carried out to determine the compressive strength value of each concrete sample in the form of a beam with a size of 200 × 200 × 120mm.This test was carried out after curing for 28 days as well as some concrete that had been coated using Crystalline.
Based on the water penetration test results as shown in Figure 3, there are different values for each type of concrete.This occurs because there are several different forming materials in each type of concrete.In addition, there are concrete samples that have large enough pores to have unbalanced values among other samples.Therefore, the data becomes anomalous data and is not included in the average calculation.
The Normal Concrete type has anomalous data in sample number one with a water penetration test value of 28 mm while sample number two and number three have water penetration test values of 50 mm and 37 mm respectively.Thus, the average penetration test value for normal concrete is 43.50 mm.In contrast to the normal concrete, the type of concrete with Type V cement has a fairly stable data in each sample, namely the water penetration test value of 48 mm, 47 mm, 50 mm respectively.Thus, the average penetration test value for concrete with Type V cement was 48.33.This figure is 11.1% lower than the water penetration test value of Normal Concrete.This may be due to the poor quality of Type V cement used in this study.The addition of a Crystalline coating layer as a second layer coat can make concrete samples resistant to water.However, the water penetration test results on this type of concrete have some non-uniform values.This is likely an error factor because when applying the Crystalline coating using a brush is not evenly distributed.

Conclusion
1.In compressive strength test, concrete with Crystalline coating and concrete with Type V cement have better average compressive strength values than normal concrete; 2. In the water penetration test, Type V Cement needs to be reviewed in its use because it has less optimal results compared to Normal Concrete.While the type of concrete with Crystalline coating, the application of the coating needs to use a better tool so that the coating adheres evenly to all parts of the concrete surface; 3. The results of compressive strength test and water penetration test of concrete with Crystalline coating are still below concrete with Type V cement.Therefore, the addition of crystalline as a concrete coating has not proven to be a good alternative to the use of Type V cement.

Suggestion
1. Application of Crystalline coating on each concrete sample using a spray gun compressor so that Crystalline can be evenly distributed on the surface of the concrete sample; ………………………….……..(2.1)Where: F'c = Compressive Strength (N/mm 2 or MPa); P = Axial pressure force (N); A = Cross-sectional area of concrete (mm 2 ).

Figure 2
Figure 2 Diagram of Concrete Compressive Strength Test Results

Figure 3
Figure 3 Diagram of Water Penetration Test Results