THE EFFECT OF MIXING SEQUENCE ON THE PROPERTIES OF CONCRETE

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Department of Environmental Design

ABSTRACT
Concrete is the most demanded material only second to water as a substance, with this, it can only be imagined that huge expense and resources have been put into it. In consideration with the aforementioned fact on concretes? demands coming in tune with the advancements of the 21st century production researches, cost free methods are being optimized to boost production efficiency. This research entitled “The effect of mixing sequence on the properties of concrete” is about the latter statement, as it deals directly with finding the most suitable mixing sequence to optimize production efficiency without any added resources. The research focused on the fresh and hardened properties of concrete. British Research Establishment (BRE) Method of mix design was used. A total of 720 cubes were cast for tests at the following ages of 7, 14, 28 and 56 days. Twenty four (24) mixing sequences were assessed. Among the mixing sequences, two standardized mixing sequences from the ASTM and ACI were chosen. It was found that samples mixed using the standard mixing sequences of the ASTM and ACI passed all the standard requirements for all properties of concrete assessed. However the samples produced using ACI mixing sequence had better hardened concrete properties when compared with the samples of concrete made using ASTM mixing sequence. All the concrete batch samples from the various mixing sequences passed the standard conditions for compacting factor and plastic density. Samples mixed using mixing sequences (22, 19 and 17) did not pass the standard condition for slump. Samples mixed using mixing sequences (14 and 17) did not pass the standard condition for air content. Samples from mixing sequence 24 had optimum compressive strengths of 23.40N/mm2, 25.52 N/mm2, 30.84 N/mm2 and 35.56 N/mm2 for 7, 14, 28 and 56 days of testing respectively and xiv passed all the standard conditions for all properties tested. It surpassed samples from the standardized mixing sequences in grade by at least 4.7% for every test age. During concrete production, with all processes, materials and proportioning considered, two sets of concrete samples from two different mixing sequences can differ in average from 0.91% to 41.85% under water absorption while two sets of concrete samples from two different mixing sequences can differ in average from 0% to 100% under abrasion resistance. From the properties of concrete tested, the various mixing sequences used have the most positive effects on plastic density followed by air content then slump and finally compressive strength. Due to the differences in the properties of concrete samples under the influence of different mixing sequence, it is recommended that good mixing sequences, when used should be consistent under a particular job. Mixing sequence 24 had optimum compressive strengths and can be used to make the best concrete. Uniformity should be checked firstly for fresh concrete properties when determining which or what mixing sequence to use.