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Below is the proceedings of the International RILEM Conference in 1996 - technical report

 

Below is the proceedings of the International RILEM Conference in 1996 - technical report

Production Methods

and Workability

of Concrete

Proceedings of the International RILEM Conference

Paisley, Scotland

June 3-5, 1996

EDITED BY

P.J.M. Bartos and D.L. Marrs

Advanced Concrete Technology Group, Department of Civil, Structural and Environmental Engineering University of Paisley, Scotland,

 

 

and

D.J. Cleland

Department of Civil Engineering, The Queen's University, Belfast, Northern Ireland

 

 

E & FN SPON An imprint of Chapman & Hall

London - Weinheim - New York - Tokyo - Melbourne - Madras


CONTINUOUS CONTROL OF FRESH CONCRETE USING THE FCT 101 TESTER

T. STEINER - Research and Consulting Institute of the Swiss Cement Industry, Wildegg, Switzerland

Abstract

The new test method provides results combining those of the traditional testing methods of fresh concrete. Advantages of the new method are the speed of the test procedure, the possibility to test concrete in-situ without removing any material, ability to carry out a number of workability tests in a rapid succession on the same sample, to store the results and print them out with a portable PC and provide complete practical test documentation.

Keywords: Fresh concrete tests, FCT-tester, workability, slump, water-cement ratio, continuous recording, computer processing, concrete temperature.

1. Introduction

Tests such as the slump, flow, compaction, Vebe and other test methods are usually used to determine the variability of the workability of a fresh concrete mix.

Such tests are described in appropriate standards and guidelines exist for use of these tests in practical production quality control. The standard tests tend to provide reproducible results and the basic tests are indispensable tools in modern concrete construction practice.

All the standard workability tests are relatively labour intensive. A considerable time usually elapses between the extraction of a test sample and the final results being available. In practice this means that the control of the workability of concrete is generally only made at intervals or at random. A systematic, virtually gap-less, continuous control of workability dependent on the process of stiffening of the cement paste and the water loss is practically impossible with the traditional methods.

Furthermore, it has to be considered that in each test in which a sample of fresh concrete is removed there is a probability of the sample not representing the in-situ concrete on the building site

Practical concrete construction requires a method, which allows judging the workability of a mix within max. 2 minutes if a fresh concrete is to be placed in a shuttering or it is to be rejected because of its low workability. Not only the consideration of easy pouring and compaction but also workability required for all finishing work which has to be undertaken must be taken in order to determine the correct workability. Concrete mixes of good workability are particularly necessary in the case of air entrained concrete, concrete with silica-fume or for concretes used for building conservation.

2. The FCT tester

The operating principle of the test is based on a determination of a torque of a rotating probe. The tester gives values for concrete with coarse aggregate up to 32 mm and a slump between 35 and 180 mm with an accuracy of + 3%. The equipment is hand-held (2.4 kg) and battery operated. The tests can be carried out in any location provided there is at least a volume of 50 litres of fresh concrete available. The calibration of the tester is very simple. The required FCT values can be determined at the same time as the fresh concrete is tested in the usual conventional manner. Depending of the requirements and problems which have to be solved several test-series may be necessary. Selection of integrated working characteristics allows the required quality parameters to be called upon in the shortest of time (slump, flow, compaction...) under the condition that the mix design has not changed. Within one minute the workability can be measured and with the established correlation factors other parameters like water-cement-ratio can be determined.

A significant advantage is that the tests can be repeated using the same batch of fresh concrete. It is therefore possible to observe the development of the stiffness of the mix. The measured values are stored in the tester and can be recalled and printed out via a PC. The quality control can be thus documented continuously.

3. Application

High performance reinforced concrete construction elements require a continuous quality control. In such cases a single non-conforming mix can cause the failure of the whole construction. Bridge decks, waterproof concrete containers, pipes, slim supporting piers and similar structures have to guarantee the required safety demands even in their weakest parts. In such circumstances it is necessary to test not just some of the concrete, selected batches only, but much more of the concrete, virtually all the mix prior to being poured into the formwork must be tested. The continuous testing should also eliminate external effects such as long transportation times, weather etc. The continuous and inexpensive monitoring proposed will always make it cheaper to reject doubtful concrete rather than accept the potential cost of repair of the failed part of a construction

Requirements and problems which have to be solved several test-series may be necessary. Selection of integrated working characteristics allows the required quality parameters to be called upon in the shortest of time (slump, flow, compaction...) under the condition that the mix design has not changed. Within one minute the workability can be measured and with the established correlation factors other parameters like water-cement-ratio can be determined.

A significant advantage is that the tests can be repeated using the same batch of fresh concrete. It is therefore possible to observe the development of the stiffness of the mix. The measured values are stored in the tester and can be recalled and printed out via a PC. The quality control can be thus documented continuously.