CONCRETE TECHNOLOGY
ENHANCING STANDARD TEST APPROACH TO BETTER REFLECT APPLICATION REQUIREMENTS by C T Tam, Department of Civil & Environmental Engineering, Na onal University of Singapore Standard test methods are intended for assessing conformity requirements. The type of test equipment and procedure are well defined for the intended purpose. The materials, rela ve propor ons and method of preparing the test specimens are clearly detailed. The test environment, eg temperature and rela ve humidity are specified, where needed. However, some, if not all of the above, may not be the actual values for prac cal applica ons on site, par cularly in concrete construc on. This presenta on provides selected examples of how the above factors may be adjusted in the standard test methods for be er correspondence to actual project requirements or a modified test procedure which leads to a be er outcome. These include the consistence in terms of degree of compactability (previously compac ng factor), passing ability of SCC in fresh concrete, the s ening mes of concrete (generally in terms of se ng mes) and the temperature issues of peak temperature (poten al DEF) and maximum temperature dieren al (poten al early thermal cracking) in hardened concrete arising from heat of hydra on of cement in the cas ng of thick concrete sec ons that may take many hours of con nuous cas ng. The enhancing of selected standard test methods with appropriate modifica ons be er relates to the actual applica on requirements and is presented. INTRODUCTION Standard test methods are intended for assessing conformity requirements. The type of test equipment and procedure are well defined for the intended purpose. The materials, rela ve propor ons and method of preparing the test specimens are clearly detailed. The test environment, eg temperature and rela ve humidity are specified, where needed. However, some, if not all of the above, may not be the actual values for prac cal applica ons on site, par cularly in concrete construc on. The quan ta ve results o en are not directly applicable to the site requirements. In the execu on of concrete structures, the performance of concrete is the actual interest. The principle of performance tes ng should be the same as in conformity tes ng. However, modifica ons in the test details together with the use of the actual cons tuents and composi on of the specified concrete for the project are used to assess the resultant performance. The above factors may be adjusted in the standard test methods for be er correspondence to actual project requirements or modified test procedure which leads to a be er outcome. This presenta on provides some examples selected to illustrate how the standard test procedures and the measurements can be modified to achieve the outcome to be er reflect applica on requirements.
density of par ally compacted concrete with the density of fully compacted concrete. The former test adopted the apparatus shown in Figure 1 to provide the same volume and the new approach is based on the same mass of concrete. The volume of fresh concrete completely filling the top hopper is dropped into the lower hopper and then into the cylindrical mould. The mass of the par ally compacted volume of concrete is then compared to the mass of a fully compacted volume of the same concrete. The compac ng factor (CF) is based on the ra o of the par ally compacted mass to that of the fully compacted mass of the same volume. A larger value of CF represents a higher degree of compac on. In lieu of comparing by mass, an alternate method to determine CF is by the volumes of the same mass. The volume of the par ally compacted concrete in the cylinder mould is compared to the volume of the same mass of fresh concrete [3,4].
DEGREE OF COMPACTABILITY For low level of consistence, the compac on of fresh concrete is formerly assessed by the compac ng factor test to BS 1881: Part 103 [1] which is now replaced by the test on the degree of compactability to BS EN 123504 [2]. In both methods, the principle is to compare the
Figure 1: Compac ng factor test apparatus [1].
Figure 2: Device providing direct CF result [3]. THE SINGAPORE ENGINEER January 2020
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