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This publication should be of interest to individuals involved in concrete failure investigations, particularly those related t o durability, and in quality control efforts aimed at assuring a durable structure. Academics, researchers, materials engineers, forensic engineers, and materials producers should all benefit from the information presented in this publication. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP191

The performance needs of the Toronto Transit Commission (TTC), for the reinforced concrete tunnel liner segments for the Toronto Sheppard Line Subway required a service life of at least 100 years. Under the contract specification for chloride diffusion, compliance with this requirement was determined by the water permeability and chloride diffusion coefficients of the concrete. The specified test procedures required up to six months for final test results, after a segment was cast. From a practical point of view, what is required is confirmation that the segments are acceptable shortly after they have been cast. An in-situ rate of absorption (sorptivity) test was modified and implemented. This paper summarizes the implementation of this simple test procedure into the QC programme to non-destructively evaluate the quality of the concrete shortly after fog curing is complete. The primary research goal of this project was to develop a service life model that utilized the initial sorptivity value as determined by the in-situ sorptivity test combined with a diffusion value established for the concrete mix. The use of service life modelling to predict performance of reinforced concrete structures exposed to chlorides is the next logical step to provide assurance of longevity for owners.

The ability of concrete to resist the ingress of chlorides, whether from deicing salts or from marine exposure, is an important factor in determining the durability of a structure. Currently in North America, there are two standardized tests for determining the ability of concrete to resist chloride penetration: the 90-Day Salt Ponding Test (AASHTO T259) and the Rapid Chloride Ion Permeability Test (AASHTO T277 or ASTM C1202). These methods have significant limitations however, mainly related to their duration and their limits of applicability. A variety of other test methods have been developed over the past decade. With the support of the U.S Department of Transportation Federal Highway Administration (FHWA), a study was undertaken to compare the more promising of these test methods and to examine their possible application as a short term test for chloride ingress, for the purpose of evaluating new mixtures and existing structures and for use as a quality control measure. Four short-term tests were conducted on eight separate concrete mixes of various qualities. The results were compared to a bulk diffusion test.

A laboratory and field test program was undertaken to determine the perfromance of a nuclear water/cement content gauge for fresh concrete. The laboratory evaluations included study of the effects such variables as air content, pozzolans, hold time, coarse aggregate, and temperature on gauge response. The laboratory testing demonstrated that the gauge is sensitive to materials compositions and other factors, and therefore must be calibrated with exactly the same materials as will be used on the job in question. With proper calibration in a laboratory setting, the cement gauge is capable of determining cement content of fresh concrete to within approximately 10 to 20 lb/yd3 (6 to 12 kg/m3). The water gauge is capable of determining water content to within approximately 2 to 4 lb/yd3 (1 to 2 kg/m3). Field tests at two locations are described. Favorable results were acheived where calibrations were carefully carried out using the same materials as to be used in actual construction. In these cases, avearge water content determinations for a series of samples using the nuclear gauge were comparable to those obtained using a microwave oven drying technique.The gauge is well-suited for use at construction sites. Technicians (having proper radiation safety training and certification) can successfully operate the gauge after a brief period of training, and the gauge can be transported in construction vehicles and set up on-site with a minimum of effort. The test period is short, requiring approximately ten minutes per sample, including consolidating of concrete into a test bucket.

The water/cementitious ratio of concrete is an important indicator of quality of concrete in the numerous ways that have been chosen to measure it. Low water/cementitious ratio concretes are high strength, low permeability, high durability and permanent concretes. It is also a property which is not frequently measured at the time of construction or on concretes which undergo distress during their service life due to the lack of standardized test methods and cheap test procedures for determining this property. In the present study, the use of electrical resistance measurements to estimate the water cementitious ratio and chloride ion diffusivity in terms of water cementitious ratio, compressive strength of concrete is explored. Both hardened and plastic concretes were studied, over a wide range of water/cementitious ratios. Supplementary cementing materials, paste volume fractions and admixture chemistries were varied as well. The results indicate that a rapid, field portable test can be used to estimate the water/cementitious ratio of plastic concrete delivered to the site, as well as samples of hardened concrete removed from structures. Use of the formation factor analogy to describe the pore system and measurements of the total pore volume allow an estimate of the transport properties of the concrete, such as diffusivity and permeability. Properties estimated by this technique are compared to those determined using the standard determination methods. The implications of using assumed pore solution characteristics are discussed. The method developed is potentially useful in both Quality Assurance and Quality Control testing of high performance structures. Additional work is required to develop a field test.