M.Sc Thesis
M.Sc Student Mozes Amiel Determination of the "Concrete Families" for Quality Control of Ready Mixed Concrete Department of Civil and Environmental Engineering Professor Katz Amnon Professor Emeritus Weissman Ishay

Abstract

The main building material for construction in Israel is concrete. The dominant property of the hardened concrete is its compressive strength. As in other processes control, the concrete quality control is performed by using statistical methods.

This modern approach requires some changes in the relevant standards and a different attitude by all the professionals who use this data about the concrete's quality.

The Israeli valid standard, SI 118 is based on the conformity definition of the concrete based on the approach of inspecting concrete lots that are supplied to each individual site.

Chapter 8 in the European standard EN 206 deals with the conformity control for the main properties of the concrete, i.e. its compressive strength, and presents a different attitude. The quality control is performed by the producer himself on the concrete produced in the concrete plant and the results are used to make the conformity decision. This attitude differs from the Israeli standard where only test results of accredited laboratories, performed on every construction element, are valid for conformity of the concrete.

Self testing by the producer changes the whole system of data collection for strength control, and might reduces the number of samples compared to the present collection system.

One method to reduce the number of samples is by using the principle of “concrete family”. A group of concrete mixes is created if they comply with certain statistical conditions. If all these conditions are complied, then samples can be collected from each of the members in the group, and the results of compressive strength are transformed to a common basis by using mathematical transformation rules. Otherwise, representative samples must be collected from each of the individual mixes leading to large number of specimens.

The goal of this work is to examine the possibility of implementation of the “concrete family” concept in the Israeli concrete industry.

All the field data of one year production were collected from two sources: concrete plants and certified laboratories.

The main conclusions are:

1. The variance of the raw materials has a large effect on the ability to keep all the mixes as a single “concrete family”.
2. Based on statistical considerations, it was found that it is very difficult to define a single "concrete family" that includes all the mixes in a concrete plant.
3. The number of mixes that consists an ideal “concrete family” is undetermined.