Impact resistance of polypropylene fibre-reinforced concrete was investigated using the repeated drop weight impact test recommended by ACI Committee 544. The results were analysed based on a statistical approach. The variation in results was examined within the same batch and between different batches. Statistical parameters were compared with reported variations in impact resistance of concrete composites reinforced with other types of fibres such as carbon and steel fibres. Statistical analysis indicated that the results obtained from this test had large variations and it is necessary to increase the number of replications to at least 40 specimens per concrete mix to assure an error below 10%. It is concluded that this test with its current procedures and recommendations should not be considered a reliable impact test. This study has highlighted the need for modifying this test in such a way as that increases its accuracy and reduces the large variation in results.

20The ACI Committee 544 repeated drop-weight impact test for concrete is often criticized for large 21 variations within the results. This paper identifies the sources of these large variations and 22 accordingly suggests modifications to the ACI test. The proposed modifications were evaluated and 23 compared to the current ACI test by conducting impact resistance tests on 40 specimens from two 24 batches of polypropylene fiber reinforced concrete (PPFRC). The results obtained from both 25 2 methods were statistically analyzed and compared. The variations in the results were investigated 1 within the same batch and between different batches of concrete. 2 3The impact resistance of PPFRC specimens tested with the current ACI test exhibited large 4 coefficients of variations of 58.6% and 50.2% for the first-crack and the ultimate impact resistance, 5respectively. The corresponding coefficients of variations for PPFRC specimens tested according to 6 the modified technique were 39.4% and 35.2%, indicating that the reliability of the results was 7 significantly improved. 8 9 It has been shown that, using the current ACI test, the minimum number of replications needed per 10 each concrete mix to obtain an error below 10% was 41 compared to 20 specimens for the modified 11test. Although such large number of specimens is not good enough for practical and economical 12 reasons, the reduction presents a good step on the development of a standard impact test. 13 14 Keywords: impact resistance; statistical variation; fiber reinforced concrete. 15 16 INTRODUCTION 17Despite the significant increase in the impact resistance of concrete due to the addition of fiber 18 reinforcement [1][2][3], researchers and designers are not able to utilize impact resistance as a design 19 parameter, simply because it cannot be fully quantified due to the lack of a standard impact test for 20 concrete. The absence of a standard impact test prompted researchers to propose their own impact 21 tests to estimate the impact resistance of concrete either quantitively or qualitatively [3][4][5][6][7]. Some of 22 these tests are relatively difficult to perform and require sophisticated equipments. However, none 23 of these tests have been claimed to be a standard test due to the lack of statistical data on the 24 variation of the results. In this regard, the ACI Committee 544 [8] has proposed a drop weight 25 impact test to demonstrate the relative brittleness and to quantify the impact resistance of fiber 26 3 reinforced concrete (FRC). The test is widely used since it is simple and economical. However, the 1 results obtained from this test are often noticeably scattered [9]. The large variation in impact 2 resistance as determined from this test is reported in the literature for different types of FRC [10][11]. 3However, large variation is a common problem in impact testing; and it is difficult to devise 4 systems that give reproducible results [7]. This might be attributed to the nature of the impact 5 process itself and the number of fact...

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In this paper, the durability of fabric formwork-based concrete made from supersulfated cement was studied. The study involved comparison of chloride and carbonation resistance, pH values, and water absorption between of surfaces of SSC, the one being cast and the other cast in fabric formwork. It was shown that the use of fabric formwork minimized the pore volume near the surface, maintained the pH values at higher profile depths and showed improved durability when compared to the mould-cast surface. Carbonation depths were reduced by approximately 35% and calculated ab sorption rates were found to be approximately 40% lower at the fabric cast surface, indicating that fabric formwork is a promising aspect towards promoting the comeback of SSC in construction.

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