AN EXPERIMENTAL STUDY OF SPRAYED MORTAR FOR REPAIRING APPLICATION

Abstract

This study is to develop mix proportions of sprayed mortar and to investigate
the performance of sprayed mortar regarding fresh and hardened properties,
including mini slump flow, setting time, sagging resistance, build-up
thickness, compressive strength, bond (pull-off) strength, drying shrinkage
and age at cracking for repairing application. The research focuses on the
maximum size of aggregate of 0.6 mm. with the addition of admixtures and
the percentage of fly ash used for cement replacement. The results have
shown that sprayed mortar with 0.01% starch ether, 0.5% water reducing
agent and 8% shrinkage compensating admixture is the optimum mix proportion
for use with cement and fly ash. The maximum build-up thickness of each
layer is 50 mm. that can be applied without sagging. The cement replacement of
40% fly ash also produces satisfactory performance including workability,
pumpability and sprayability. The compressive strength, bond strength, drying
shrinkage and age at cracking of this mix are 38 MPa, 1.81 MPa, 145
millionths (expansion) at 28 days and no cracking after 60 days, respectively.
The hardened performance is higher when mortar is sprayed compared with
hand application. For demonstration, this sprayed mortar is applied to repair
a damaged column. After repairing, ultrasonic pulse velocity (UPV) is used
to check the quality of concrete. The result shows that the quality of concrete is
good. Additionally, the cost of this sprayed mortar is much lower than the
commercial product with similar properties and application. Therefore, the
development of sprayed mortar with fly ash used for cement replacement
has been satisfied with high performance and low cost for repairing
application.