EXPERIMENTAL STUDY OF SELF-CURING CONCRETE

Page 1 EXPERIMENTAL STUDY OF SELF-CURING CONCRETE Xiao Yuan, Xiao Peng, Liu Yi, Xiao Yong 1 School of Civil Engineering, Faculty of Engineering, Wuhan University, Wuhan, People Republic of China 2 School of Civil Engineering, Faculty of Engineering, Wuhan University, Wuhan, People Republic of China 3,4 School of Engineering Science, University of Science and Technology of China, People Republic of China ____________________________________________________________________________________ *Corresponding Author: Xiao Yuan Article Received: 11-11-19 Accepted: 24-02-20 Published: 27-03-20


INTRODUCTION
There is increased usage of concrete and it leads to the rapid increase in concrete technology. Internal curing of concrete is a new concept and has gained increased popularity (Mather, 2001;Shetty, 2000). The idea of internal curing concrete is that such concrete maintains good level of moisture contents within itself during its early stages which enable development of desired properties (IS 456:2000). This maintenance of moisture leads during the early stages leads to the higher level of performance, durability, and hardness of such concrete. However, because of some difficulties such as lack of enough water, the good curing is not achievable all the times. identification of self-curing agent is the prime concern of many researchers. One solution is the polyethylene-glycol which enable minimum water evaporation due to the decreased surface tension of the water (Bentz, Lura, & Roberts, 2005). This enable greater water retention and curing. Generally, water-soluble polymers or polyethylene Glycol are considered as self-curing concrete agent. In this study, we investigate Polyethylene Glycol and its use as self-curing concrete. The study is experimental in nature and details are provided below.

EXPERIMENT DETAILS Material
Portland Pozzolana cement is used in the study along with fine aggregate obtained from river bed, and angular coarse aggregate with maximum size of 25 mm. All material used in the study are fulfilling the standard requirements.  We used two separate concrete mixes with same w/c ratio. We added self-curing agent in one of the mix, while, the other mix remained unadded. The compacting factor value and the slump value for the both types of concrete are provided in table 3.

Non-Destructive Test
For establishing the compressive strength of the concrete, Schmidt rebound hammer test is conducted. The test was performed while keeping rebound hammer in vertical position with 175 mm cube specimen.

Compression and Split Tensile Strength
Cube of 175 by 175 mm size and cylinder of 175 diameter belonging to the self-curing and the conventional concrete were casted. We used a steel tamping rod of about 18 mm diameter and 700 mm length for blowing each layer with 30 blows. The conventional based specimen was permitted to get dry for 24 hours after casting. As per the requirements, the water was sprinkled at regular time interval for both the cubes and the cylinder. For self-curing specimen, no external curing such as sprinkling was used. The strength related tests were performed for both types of specimen after 3, 7, and 28 days passed. Water Absorption Test 90 days curing time was used for immersing the cylinder after casting. The specimens were later dried for 24 hours at the temperature of about 100 centigrade until the mass get to the constant level which was used to calculate the dry weight of the cylinder. Later, this was kept in hot water at about 9-centigrade for 4 hours and its weight was taken as the wet weight of the cylinder labelled as W2. The percentage of the water absorption was taken as the W1 deducted from W1 and divided by W1.

Water Sorpitivity Test/Durability Test
Water sorptivity test was conducted for measuring the rate of water absorption. Cylinder of 100 mm and 50 mm height were used for both the conventional and self-curing concrete. These specimens were dried for 24 hours at the 100 centigrade and left to cool in dry conditions for another 24 hours. The test was conducted by placing one circular surface of the specimen to be in contact with water at 5 mm depth. The rest of the part of the specimen was coated with high quality water proofer for creating unidirectional flow pattern through the concrete specimen. These tests were conducted on both type of samples at the age of 28 days for assessing the absorption rate of the water at interval of 30 minutes, 60 minutes, 90 minutes, and 120 minutes, 150 minutes, and 180 minutes.

RESULTS
The results are as follows; For NDT test for M10 at the age of 3 days, the test statistics for cube for self-cured is 14, fullycured is 11, and sprinkler-cured is 10. The test statistics for cylinder for cube for self-cured is 12, fully cured is 10, and sprinkler-cured is 9.  For NDT test for M20 at the age of 3 days, the test statistics for cube for self-cured is 15, fullycured is 13, and sprinkler-cured is 11. The test statistics for cylinder for cube for self-cured is 13, fully cured is 12, and sprinkler-cured is 9. For NDT test for M30 at the age of 3 days, the test statistics for cube for self-cured is 16, fullycured is 14, and sprinkler-cured is 10. The test statistics for cylinder for cube for self-cured is 14, fully cured is 12, and sprinkler-cured is 8.

Figure 4: NDT for 7 Days-M10
For NDT test for M10 at the age of 7 days, the test statistics for cube for self-cured is 22, fullycured is 20, and sprinkler-cured is 18. The test statistics for cylinder for cube for self-cured is 20, fully cured is 19, and sprinkler-cured is 16.  For NDT test for M20 at the age of 7 days, the test statistics for cube for self-cured is 24, fullycured is 20, and sprinkler-cured is 26. The test statistics for cylinder for cube for self-cured is 22, fully cured is 19, and sprinkler-cured is 22.  Table 9: NDT for 7 Days-M30

Figure 6: NDT for 7 Days-M30
For NDT test for M30 at the age of 7 days, the test statistics for cube for self-cured is 16, fullycured is 14, and sprinkler-cured is 10. The test statistics for cylinder for cube for self-cured is 14, fully cured is 12, and sprinkler-cured is 8.  For NDT test for M10 at the age of 28 days, the test statistics for cube for self-cured is 44, fullycured is 36, and sprinkler-cured is 38. The test statistics for cylinder for cube for self-cured is 40, fully cured is 34, and sprinkler-cured is 34.  For NDT test for M20 at the age of 28 days, the test statistics for cube for self-cured is 44, fullycured is 38, and sprinkler-cured is 42. The test statistics for cylinder for cube for self-cured is 40, fully cured is 32, and sprinkler-cured is 40.

Figure 10: Compressive Strength for 3 Days-M10
For compressive strength test for M10 at the age of 3 days, the test statistics for cube for selfcured is 10, fully-cured is 12, and sprinkler-cured is 12. The test statistics for cylinder for cube for self-cured is 10, fully cured is 10, and sprinkler-cured is 8.  For compressive strength test for M20 at the age of 3 days, the test statistics for cube for selfcured is 14, fully-cured is 12, and sprinkler-cured is 14. The test statistics for cylinder for cube for self-cured is 12, fully cured is 10, and sprinkler-cured is 12.  For compressive strength test for M30 at the age of 3 days, the test statistics for cube for selfcured is 16, fully-cured is 16, and sprinkler-cured is 16. The test statistics for cylinder for cube for self-cured is 14, fully cured is 14, and sprinkler-cured is 12.  For compressive strength test for M10 at the age of 7 days, the test statistics for cube for selfcured is 14, fully-cured is 16, and sprinkler-cured is 18. The test statistics for cylinder for cube for self-cured is 14, fully cured is 14, and sprinkler-cured is 16.  For compressive strength test for M20 at the age of 7 days, the test statistics for cube for selfcured is 28, fully-cured is 30, and sprinkler-cured is 32. The test statistics for cylinder for cube for self-cured is 24, fully cured is 26, and sprinkler-cured is 28.  For compressive strength test for M30 at the age of 7 days, the test statistics for cube for selfcured is 32, fully-cured is 28, and sprinkler-cured is 30. The test statistics for cylinder for cube for self-cured is 30, fully cured is 26, and sprinkler-cured is 26.  For compressive strength test for M10 at the age of 28 days, the test statistics for cube for selfcured is 42, fully-cured is 44, and sprinkler-cured is 50. The test statistics for cylinder for cube for self-cured is 38, fully cured is 40, and sprinkler-cured is 46.  For compressive strength test for M20 at the age of 28 days, the test statistics for cube for selfcured is 44, fully-cured is 44, and sprinkler-cured is 48. The test statistics for cylinder for cube for self-cured is 38, fully cured is 36, and sprinkler-cured is 42.

Figure 19: Split Tensile Strength for Cylinder 3 Days-M10
For split strength test for M10 at the age of 3 days, the test statistics for cube for self-cured is 0.8, fully-cured is 0.8, and sprinkler-cured is 1. The test statistics for cylinder for self-cured is 0.6, fully cured is 0.6, and sprinkler-cured is 0.8.

Figure 20: Split Tensile Strength for Cylinder 7 Days-M10
For split strength test for M10 at the age of 7 days, the test statistics for cube for self-cured is 1.2, fully-cured is 1.4, and sprinkler-cured is 1.6. The test statistics for cylinder for self-cured is 1.2, fully cured is 1, and sprinkler-cured is 1.2.  For split strength test for M10 at the age of 28 days, the test statistics for cube for self-cured is 3.2, fully-cured is 3.4, and sprinkler-cured is 3.6. The test statistics for cylinder for self-cured is 2.8, fully cured is 3, and sprinkler-cured is 3.2.

Figure 22: Split Tensile Strength for Cylinder 3 Days-M20
For split strength test for M20 at the age of 3 days, the test statistics for cube for self-cured is 1.2, fully-cured is 0.8, and sprinkler-cured is 1. The test statistics for cylinder for self-cured is 0.8, fully cured is 0.8, and sprinkler-cured is 1.

Figure 23: Split Tensile Strength for Cylinder 7 Days-M20
For split strength test for M20 at the age of 7 days, the test statistics for cube for self-cured is 1.6, fully-cured is 1.2, and sprinkler-cured is 1.2. The test statistics for cylinder for self-cured is 1.4, fully cured is 1, and sprinkler-cured is 1.  For split strength test for M20 at the age of 28 days, the test statistics for cube for self-cured is 2.4, fully-cured is 2.2, and sprinkler-cured is 2.2. The test statistics for cylinder for self-cured is 2.2, fully cured is 2, and sprinkler-cured is 2.2.    For water absorption test for M10, the test statistics is as follows. For sprinkler, after 30 minutes is 0.02; after 60 minutes is 0.05; after 90 minutes is 0.06; after 120 minutes is 0.07; after 150 minutes is 0.08; and after 180 minutes is 0.09. For full-curing, after 30 minutes is 0.03; after 60 minutes is 0.05; after 90 minutes is 0.07; after 120 minutes is 0.08; after 150 minutes is 0.09; and after 180 minutes is 0.09. For self-curing, after 30 minutes is 0; after 60 minutes is 0.01; after 90 minutes is 0.02; after 120 minutes is 0.03; after 150 minutes is 0.04; and after 180 minutes is 0.05.  For water absorption test for M20, the test statistics is as follows. For sprinkler, after 30 minutes is 0.03; after 60 minutes is 0.04; after 90 minutes is 0.05; after 120 minutes is 0.06; after 150 minutes is 0.07; and after 180 minutes is 0.08. For full-curing, after 30 minutes is 0; after 60 minutes is 0.01; after 90 minutes is 0.02; after 120 minutes is 0.04; after 150 minutes is 0.05; and after 180 minutes is 0.07. For self-curing, after 30 minutes is 0; after 60 minutes is 0; after 90 minutes is 0.01; after 120 minutes is 0.02; after 150 minutes is 0.03; and after 180 minutes is 0.04.  For water absorption test for M30, the test statistics is as follows. For sprinkler, after 30 minutes is 0; after 60 minutes is 0.01; after 90 minutes is 0.03; after 120 minutes is 0.04; after 150 minutes is 0.05; and after 180 minutes is 0.07. For full-curing, after 30 minutes is 0; after 60 minutes is 0; after 90 minutes is 0.02; after 120 minutes is 0.03; after 150 minutes is 0.04; and after 180 minutes is 0.05. For self-curing, after 30 minutes is 0; after 60 minutes is 0.01; after 90 minutes is 0.02; after 120 minutes is 0.03; after 150 minutes is 0.04; and after 180 minutes is 0.05.

CONCLUSION
The results of NDT test, compression and split tensile strength test, and water absorption test based on the 3 days, 7 days, and 28 days for 3 graded material shows that overall self-curing concrete shows better absorption and strength compared to the sprinkler and fully cured concrete. Furthermore, the comparison also shows that cube shows better strength for all samples compare to the cylinder. Our results confirm the previous studies finding which shows that self-curing concrete is superior in quality and possess desirable qualities such as hardness, durability, and better performance. Thus, this study recommends making greater use of self-curing concrete compare to the traditional concrete.