Near surface concrete

Construction and Building Materials 15 Ž2001. 65 79

Why assess the properties of near-surface concrete?
A.E. LongUa, . , G.D. Hendersonb, F.R. Montgomery c
Faculty of Engineering, The Queen’s Uni¨ ersity of Belfast, Belfast, Northern Ireland, UK b Dr I.G. Doran and Partners, Belfast, Northern Ireland, UK c School of Ci¨ il Engineering, The Queen’s Uni¨ ersity of Belfast, Belfast, NorthernIreland, UK
a

U

Abstract The deterioration of concrete structures is a major problem in many countries throughout the world. This has prompted the search for methods of predicting the service life of both existing and new structures. Current prediction methods are still in their infancy and, before they can be used with confidence, more reliable information on the properties of the concrete inthese structures will be required. In this paper a range of test methods for determining the strength and transport properties and the extent of corrosion are critically reviewed. Whilst all provide useful information the ability to measure the transport properties has been shown by many researchers to give the most reliable indication of the likely durability. In spite of this it is recommendedthat an holistic overview is adopted as no single test is sufficiently reliable at present. Using such an approach, durability-based design criteria can be developed for concrete and the remaining life of existing structures estimated. 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Transport Building technology; Chloride ingress; Concrete; Durability; Moisture content; Permeability;Service life; Sorptivity; Strength;

1. Introduction Within Europe it has been estimated that the value of the infrastructurerbuilt environment represents approximately 50% of the national wealth of most countries. Because of this the degree and rate of degradation of the built environment in Europe is of enormous economic and technical importance. When it is borne in mind that approximately 50% ofthe expenditure in the construction industry in Europe is spent on repair, maintenance and remediation then it is evident that even marginal savings could result in the release of substantial funds for new developments. One specific area which is assuming an increasing proportion of the costs in most countries is the premature deterioration of concrete structures. It has now been recognised thatUU

Corresponding author. Tel.: q44-1232-245-133; fax: q44-1232663-754. E-mail address: a.long@qub.ac.uk ŽA.E. Long..

this lack of durability, relative to that anticipated, needs to be addressed as a matter of urgency. A similar situation exists in countries where much of their development has taken place in this century. However, the proportion of concrete structures is relatively higherthan in Europe. For example, in the United States conservative estimates of the current cost to rehabilitate deteriorating concrete structures are in the 100 billion dollar range. It is evident, therefore, that the deterioration of concrete structures is a major problem in almost all parts of the world. The deterioration of concrete with time has been described graphically Žsee Fig. 1. by Sommervillew1x. Most concrete will follow a durability performance pattern similar to curve 2 in which there is significant deterioration with time but intermittent maintenance can temporarily restore the situation before further deterioration occurs. Minimal deterioration Žcurve 1. may not be achievable without high initial expenditure but a catastrophic loss of durability of the form shown0950-0618r01r$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 0 0 . 0 0 0 5 6 - 8

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A.E. Long et al. r Construction and Building Materials 15 (2001) 65 79

Fig. 1. Loss of durability with time w1x.

in curve 3 seldom, if ever, occurs. Because of the gradual nature of this loss of durability it is evident that much useful information could be obtained...