Influence of the molding process and different surface regularization methods on the compressive strength of concrete specimens

Abstract

Concrete is one of the most important material for civil construction, given its high applicability. C Compressive strength (fc) is one of the main parameters to evaluate the concrete quality. Concrete of the same mixing volume may vary even with the same materials preparation. Concrete specimens molding, and its surface regularization contribute to these variations that are often hard to measure. Therefore, this paper aims to determine the variations in compressive strength of concrete, simulating different processes for casting, initial curing and surface treatment. In stage 1, the specimens were subjected to five surface treatment types, resulting in variations of 30% for concrete fc, whereas grinding specimens reached the highest 28-day compressive strength, so they were carried over to the next stage. In stage 2, specimens were produced as per ABNT NBR 5738 (2015) and with induced errors in casting and initial curing. The specimen produced according to the standard achieved the second-best result, whose 28-day fc was3% lower than that of the similar method, despite leaving the specimen uncovered for the first 24 hours after casting. Specimens produced in metal cylinder form works shows higher results than those produced in polyvinyl chloride molds (PVC).

Dynamic responses of reinforced concrete slabs under sudden impact loading

“…After completing the curing period of 28 days, the cubic samples are tested under axial load in the press machine to decide the compression strength of concrete (Lerner et al, 2020). Ultimately, average cubic compression strength value is determined as 31.7 MPa.…”

Influence of the preparation of the cylindrical specimen surface and approach analysis on the test value of compressive strength

“…ASTM C1231/C1231M:2010 13 specifies capping with neoprene sheet and also allows it to be reused, but it is necessary to perform qualification tests on the sheet. 14 The use of capping with neoprene sheet has the disadvantage that they are well suited to standardized sizes and wellmatched caps diameters. For drilled cores, diameters may fluctuate, resulting in gaps between the specimen wall and the sheet, and in turn leading to neoprene extrusion and creating uneven loading on the specimen plane.…”

“…Nowadays, capping with neoprene sheet is on the rise in Brazil, because it is a more practical method. ASTM C1231/C1231M:2010 13 specifies capping with neoprene sheet and also allows it to be reused, but it is necessary to perform qualification tests on the sheet 14 . The use of capping with neoprene sheet has the disadvantage that they are well suited to standardized sizes and well‐matched caps diameters.…”

“…Previous studies have shown significant differences in the results of resistance of specimens that have undergone different methods of tops preparation. 14,15 Furthermore, some methods have obtained a greater dispersion results than others, and some tests were even considered deficient because of this variation, according to performance evaluation test of NBR 5739: 2018 1,9,17,18 MARCO; REGINATO; JACOSKI, 2003 apud 9,19 ; RUDUIT, 2006 apud. 1,14,15,20 The demand for greater rigor in technological control in the materials used in major engineering works has been growing in line with the complexity of structural projects.…”

“…14,15 Furthermore, some methods have obtained a greater dispersion results than others, and some tests were even considered deficient because of this variation, according to performance evaluation test of NBR 5739: 2018 1,9,17,18 MARCO; REGINATO; JACOSKI, 2003 apud 9,19 ; RUDUIT, 2006 apud. 1,14,15,20 The demand for greater rigor in technological control in the materials used in major engineering works has been growing in line with the complexity of structural projects. In many situations, it is necessary that the tests are able to express the influence that the composition of different materials and additions have on the concrete.…”