Determination of water/cement-ratio of cement

Abstract

Water/cement-ratio (w/c-ratio) is an important factor affecting quality of the concrete, which has motivated engineers to do research on determining the w/c-ratio. The traditional way to estimate the w/c-ratio by weighing the cement and water from mix design. The estimated results are usually not accurate as the other factors affect the accuracy such as moisture in the aggregates and water added in the construction site. In this thesis other methods are investigated to determine the w/c-ratio of fresh and hardened concrete.

The research was carried out in the literature review which consisted of an effect of hydration process, a source of water in the concrete, workability of the concrete as well as w/c-ratio effect on the strength of the concrete. The laboratory work consisted of the preparation of nine concrete with three different w/c-ratio and each w/c-ratio is divided into three categories of air content ranging from 2% to 10% by volume. Different measurement methods are explained in the experimental part to determine the w/c-ratio of fresh and hardened concrete. Three methods are exploited to determine w/c-ratio of fresh concrete and one method for hardened concrete. The methods utilized in the fresh concrete are hydro-mix, SONO-WZ and microwave oven. The capillary suction method is used for the hardened concrete.

Based on the result and calculation, Hydro-mix shows moisture content in the real-mixing time and it shows good results with higher air content. SONO-WZ is a portable measuring device it shows good results with higher w/c-ratio and concrete with the air content in the range of 2% to 7%. SONO-WZ is not a suitable device for the 9–10% air content concrete that is because the air gaps in the high air content concrete which affect the flow of dielectric current. Microwave shows reliable results, however, the results are less than the actual w/c-ratio because there is still some entrapped air left in the sample.

Digitalization measurement system plays an important role in modernizing the quality control of concrete. It is beneficial to measure the workability, moisture content and air content of concrete in all phases of concrete production. These measurement technologies measure the properties of concrete in real-time with minimal effort and less supervision.