Marios Soutsos

Dielectric properties of concrete and their influence on radar testing

Sub-surface radar is becoming increasingly popular as an inspection method. Interpretation can be enhanced if uncertainties about the dielectric properties of the concretes under investigation are removed. The need for reliable data to identify possible variations of the dielectric properties of different concrete mixes and their condition on site has led to a systematic laboratory based experimental programme under the auspices of a major European Commission (Brite-Euram III Framework 4) funded project. Some key results from this recently completed work are presented in this paper with practical implications related to field surveys of structural concrete.

Assessing bridge pier scour by radar

Detection of river-bed scour around bridge piers represents a major current problem for engineers both in the UK and internationally. Techniques using boat-mounted impulse radar survey equipment have been suggested as a potentially viable solution to the problem. A programme of systematic laboratory model tests has been undertaken to examine the influences of pier and hole geometry upon measured radar response. These tests have been supplemented by field trials on real scour holes. Results from both laboratory and field studies have been used to validate numerical models developed using ray-tracing and finite difference techniques.

Reliability of partially-destructive tests to assess the strength of concrete on site

Abstract The range of available tests for assessing the strength of insitu concrete based on measurements of surface zone properties is examined, together with developments in supporting documentation. Attention is concentrated upon a number of recent research programmes, including work undertaken as part of the European Concrete Building Project. These focus primarily upon pull-out and pull-off techniques, and encompass applications to early age strength assessment, lightweight and high strength concretes, and testing of repairs.

Fast-Track Construction with Slag Cement Concrete: Adiabatic Strength Development and Strength Prediction

The early-age strength development of concrete containing slag cement has been investigated to give guidance for its use in fast-track construction. Measurements of temperature rise under adiabatic conditions have shown that high levels of slag cement-for example, 70% of the total binder-are required to obtain a significant reduction in the peak temperature rise. Despite these temperature rises being lower than those for portland cement mixtures, however, the early-age strength under adiabatic conditions of slag cement concrete can be as high as 250% of the strength of companion cubes cured at 20 °C (68 °F). The maturity and, hence, strength development were calculated from the adiabatic temperature histories based on several maturity functions available in the literature. The predicted strength development with age was compared with the experimental results. Maturity junctions that take into account the lower ultimate strengths obtained at elevated curing temperatures were found to be better at predicting the strength development.

Selection and characterisation of geological materials for use as geopolymer precursors

Geopolymer binders are generally formed by reacting powdered aluminosilicate precursors with alkali silicate activators. Most research to date has concentrated on using either pulverised fuel ash or high purity dehydroxylated kaolin (metakaolin) in association with ground granulated blast furnace slag as the main precursor material. However, recently, attention has turned to alternative calcined clays that are abundant throughout the globe and have lower kaolinite contents than commercially available metakaolins. Due to the lack of clear and simple screening protocols enabling assessment of such geological resources for use as precursors in geopolymer systems, the present paper presents results from experimental work that was carried out to develop a functional binder using materials containing kaolinite taken from the Interbasaltic Formation of Northern Ireland. The influence of mineralogy has been examined, and a screening process, using three Interbasaltic materials as examples, that will assist in the rapid selection of suitable geopolymeric precursors from such materials is outlined.

Fast Track Construction with High-Strength Concrete Mixes Containing Ground Granulated Blast Furnace Slag

The early age strength development of concretes containing ground granulated blast furnance slag (GGBS) at cement replacement levels of 20, 35, 50 and 70% have been investigated to give guidance for their use in fast track construction. 28-day target mean strengths for all concretes was 100 MPa. Although supplementary cementitious materials like ggbs are economical, their use has not gained popularity in fast track construction because of their slower strength development at early ages and at standard cube curing temperatures. There are however indications that supplementary cementitious materials are heavily penalized by the standard cube curing regimes. Measurements of temperature rise under adiabatic conditions have shown that high levels of cement replacement by ggbs, e.g. 70% are required to obtain a significant reduction in the peak temperature rise. However, despite that these temperature rises are lower than those of portland cement mixtures they are still sufficient to provide the activation energy needed for the reaction of ggbs to “kick-in” earlier. The early-age strength of companion cubes cured at 20 degrees. The high early age temperatures are shown to be especially beneficial to ggbs concretes. Maturity measurements will be needed in order to take advantage of the enhanced in-situ early age strength development of ggbs concretes. The contractor needs to be able to confirm that the actual strength of the concrete in the structure at the rime of formwork removal exceeds a certain compressive strength. Maturity functions like the Nurse-Saul and the Arrhenius equation have been examined for their applicability to ggbs concretes. Activation energies, required as input for the Arrhenius equation, have been determined according to ASTM C1074-98.

Estimation of on-site compressive strength of concrete

The finding that concrete strength in a structure was not correctly described by the strength of specimens moulded and stored under controlled standard conditions, led to the study of the relation between actual and potential strength of concrete.

Study of fibre distribution and orientations in UHPFRC by electrical resistivity and mechanical tests

ABSTRACT This paper presents experimental tests carried out on steel fibre reinforced concrete samples, including mechanical tests as well as non-destructive technique (electrical resistivity) and non destructive technique on cores (X-ray). Electrical resistivity measurements are done as a blind test, to characterise the electrical anisotropy and deduce the distribution and the orientation of fibres. These results are compared to X-ray imaging to check the quality of the non destructive evaluation. Then, flexural and compressive strength are measured on specimens to assess the influence of fibre distribution on the concrete properties.

Pullout test correlations and in-place strength assessment : The European concrete frame building project

A full-scale, seven-story, reinforced concrete building frame was constructed in-place at the Building Research Establishments Cardington Laboratory, which encompassed a range of different concrete mixtures and advanced construction techniques. This provided an opportunity to assess in-place nondestructive test methods, namely the pullout test, and more specifically the Danish version, which has been known as the Lok test, on a systematic basis during the construction of the building. It was used in conjunction with both standard and temperature-matched cube specimens to assess its practicality and accuracy under site conditions. Strength correlations were determined using linear and power function regression analysis. Strength predictions from these were found to be in very good agreement with the compressive strengths of temperature-matched cube specimens. When a general correlation is used, however, estimates for compressive strength are likely to have 95% confidence limits of around ′20% of the mean value of four results.

Strength development of GGBS and fly ash concretes and applicability of fib model code’s maturity function - A critical review

Abstract This paper is the joint work of working group 4 of the RILEM TC 238-SCM and the fib Task Group 4.6. It was the aim of this literature study to quantify the effect of ground granulated blast furnace slag (GGBS) and silicious fly ash (sFA) on strength development of concrete. For the strength development the approach of the fib Model Code was chosen, which is based on an e-function that can be adapted to the strength development of an individual binder by selecting the so-called s-value based on the strength class of the Portland cement used. No guidance is provided for s-values for supplementary cementitious materials (SCMs). In order to determine the s-values for mixes with SCMs, a database was set up with results of material testing from literature. A relationship between s-values and w/b plus SCM/b ratios has been determined. This has been tested on laboratory cast specimens with 50 and 30% cement replacement with GGBS and FA respectively. These were cured at 20 °C. The s-values from this relationship were compared to those obtained from regression analysis and they were found to be satisfactory. This increased confidence in their use for predicting the strength development of other curing regimes, i.e. adiabatically cured concrete cubes, using the maturity function in the fib Model Code. Predictions of the effect of curing temperature, i.e. the adiabatic temperature history, on the strength development were again satisfactory. These were not significantly affected by the fib model code’s use of one value of “apparent” activation energy.