Microhardness testing of fiber-reinforced cement paste

\Microhardness testing of polyolefin fiber-reinforced Type III cement paste was performed Type III cement with two water-cement ratios (w/c) (0.38 and 0.46) was tested. For 0.38 w/c cement aged for 7 days, the mean Vickers mi crohardness found with a 0.981 N load was 620 MPa. For 0.46 w/c cement, the mean HV100 (Vickers hardness with 100 gf load) value was determined to be 435 MPa. It was shown that the Vickers microhardness data obtained at both w/c were not normally distributed, but were instead distributed according t o a log-normal distribution. The data at each w/c, however, displayed the s ame mean and variance at 95% confidence, as determined by the Kruskal-Walli s test. The indentation size effect (ISE) teas quantified and the exponent n was found to be 2.24 while the loud necessary to give a 2 mu m indentatio n diagonal K-L was 0.062 N. The minimum edge-to-edge distance between inden tations at which the indentations did not affect each other was measured an d found to be less than 12.5 mu m which was the smallest distance that L co uld be measured with the microhardness tester utilized Also the Young's mod ulus was estimated from Knoop microhardness tests, and was found to be appr oximately 11 GPa for w/c = 0.38, and 18 GPa for w/c = 0.46, although there was no statistical difference between the two values at 95% confidence. The second part of the experimental work consisted of microhardness testing in the interfacial transition zone (ITZ) of polyolefin fiber-reinforced Ty pe III cement paste The Knoop microhardness of the ITZ was measured using 0 .245 N load. The mean Knoop microhardness HK25 of the bulk paste was found to be 542 MPa. Within the ITZ, a statistically less hard region was found t o exist approximately 40 to 65 mu m from the polyolefin fiber surface. The mean HK25 of this region teas 393 Il MPa. The region less than 40 mu m from the surface could not be investigated due to the indenter head impinging o n the fiber .