HOMOGENEITY CHANGE OF THE CONCRETE STRENGTH IN MONOLITHIC CONSTRUCTION

Abstract

There is a comparative analysis of 28 days compressive strength of grade C50/60 concrete made either of a mix at a concrete plant or of a mix after delivery to the construction site or after hardening in concrete columns of cast-in-place concrete frame building.
It is established that while designing composition of concrete it is necessary to take into account the variation coefficient of concrete produced at a particular plant. The variation coefficient of concrete plays an important role in structural design, because this value depends on value of the minimum required strength of concrete.
The paper investigates changes in variation coefficient and average strength of concrete molded and cured in different conditions and from different manufacturers in Kyiv.
The method of analysis of statistical data obtained for a certain period revealed the difference in compressive strength of concrete from different concrete plants in Kyiv, which supplied the concrete mix to construction site. The results are influenced by many factors including practices of workflow when producing concrete mix and calculating the minimum required strength of ready-mix concrete.
Based on the obtained results and observations, recommendations are given regarding the care of high-strength concrete during the hardening in monolithic reinforced concrete structures of residential or industrial buildings as well as attention is drawn to the details of concrete hardening due to concreting conditions in summer and winter. The identity of pouring the concrete mix in the formwork and compaction in all structures was also monitored.
Experimental data of a number of concrete plants in Kyiv were obtained to determine the intra-batch index of compressive strength of concrete and variation coefficient in accordance with current regulations of Ukraine regarding summer and winter construction at all stages of concrete production.