| Shrinkage in cementitious materials leads to material cracking and eventually shorten the life of the structure.One way to address this problem is to add expansive agent to reduce shrinkage.Another way is to add Superabsorbent polymers(SAP),which has the ability to absorb large amount of water.In this study,both expansive agent and SAP are investigated for their combined effects on mechanical and cracking properties.This study evaluates:1.The effect and proposes to compare three different types of expansive agents(HEA,SY-G,and UEA)in regard to cracking properties in cement mortars.2.The effects of combined expansive agents and Superabsorbent polymers(SAP)on mechanical properties and crack resistance.Three designs of expansive agents HEA,SY-G and UEA are introduced in cement mortar at 2%,4%,6 %,8%,10 % and 12 % by cement weight.Another design is to have expansive agents HEA and SY-G in mortar at 2 %,4%,6%,8%,10% and 12% by cement weight combined with Superabsorbent polymers(S-AP)of 0.5% cement mass.Five experiments specified in this study are: 1.Fluidity Test or Flow Test;2.Compressive Strength Test;3.Flexural Strength Test;4.Restrained Ring shrinkage Test and 5.Restrained externally squared eccentric ring shrinkage test.The main results are as follows:In the case of single admixture,the three expansion agents can improve the fluidity of the fresh mortar;from the strength results of the 7d and 28 d mortars,the three expansion agents have enhanced strength except for UEA.The order of high to low is SY-G,HEA;the effect of adding 4% of SY-G expansion agent in mortar is better than other expansion agents,the flexural strength of mortar 28 d can reach 9.2MPa,and the compressive strength reaches 76.7MPa.In terms of cracking time,compared with the ordinary mortar,the SY-G type expansion agent significantly delayed the cracking time of the ring specimen and the outer inner circle eccentric specimen,while the mortar with HEA and UEA type expansion agent showed shorter cracking time.In the case of combining SY-G with SAP,the result showed that the compressive and flexural strength are less than the case with only SY-G.It is true for the case of combining HEA with SAP.As for the cracking time is concerned,the case of combining SY-G with SAP yields a shortened cracking time in comparison with the case with SY-G only.It is true for the case of combining HEA with SAP.Based on these results,the following preference is concluded in the effects of the expansion agent on controlling cracking: SY-G>HEA>UEA.It is not recommended that SAP and the expansion agents are used simultaneously in concrete for the purpose of reducing shrinkage and delaying cracking. |
