Title:
Microhardness Testing of Fiber-Reinforced Cement Paste
Author(s):
William M. Cross, Kiran H. Sabnis, Lidvin Kjerengtroen, and Jon J. Kellar
Publication:
Materials Journal
Volume:
97
Issue:
2
Appears on pages(s):
162-167
Keywords:
cement pastes; fibers. Microhardness; reinforcing materials
DOI:
10.14359/819
Date:
3/1/2000
Abstract:
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 microhardness found with a 0.981 N load was 620 MPa. For 0.46 w/c cement, the mean HV100 (Vickers hardness with 100 g f 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 to a log-normal distribution. The data at each w/c, however, displayed the same mean and variance at 95% confidence, as determined by the Kruskal-Wallis test. The indentation size effect (ISE) was quantified and the exponent n was found to be 2.24, while the load necessary to give a 2 mm indentation diagonal KL was 0.062 N. The minimum edge-to-edge distance between indentations at which the indentations did not affect each other was measured and found to be less than 12.5 mm, which was the smallest distance that could be measured with the microhardness tester utilized. Also, the Young’s modulus was estimated from Knoop microhardness tests, and was found to be approximately 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 Type 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 to exist approximately 40 to 65 mm from the polyolefin fiber surface. The mean HK25 of this region was 393 MPa. The region less than 40 mm from the surface could not be investigated due to the indenter head impinging on the fiber.