Ultrasonic testing of a reinforced concrete member by means of the Pundit apparatus isaffected by the steel bars embedded in the concrete. A n investigation of the effects of the reinforcement has been made, using the bar diameter and the concrete strength as the variables. It is found that the steel bar appears to act compositely with the surrounding concrete in transmitting ultrasonic pulses. The effective pulse velocity is somewhat between the pulse velocities in the two separate media, and varies with the diameter of the bar and the pulse velocity in the concrete. A n empirical formula for the efective pulse velocig is proposed. O n the basis of this formula and further theoretical consideration, the zone of steel influence is defined. A correction factor is derived whereby the measured pulse velocity in a concrete-steel medium is adjusted to give the pulse velocity in the plain concrete. Notation a perpendicular distance from centre-line of steel d diameter of steel bar k correction factor for pulse velocity in concretesteel medium I shortest distance (direct path) between transducers t transit time V, pulse velocity in concrete V, effective pulse velocity in concrete-steel V, pulse velocity in steel 7 pulse velocity ratio = V,N, bar to nearest edge of transducer medium *Senior Lecturer in Civil Engineering

Abstract:The main objective was to develop mix designs for concrete incorporating minimally processed reclaimed asphalt pavement (RAP) materials to be used in the Florida Concrete Test Road. The laboratory program was conducted in two phases. Phase I involved testing of twelve (12) trial mixes to identify feasible mixes which could meet the Florida Department of Transportation (FDOT) specification requirements for pavement concrete. Based on the preliminary test results from the trial mixes, ten (10) production mixes were identified and evaluated more extensively in Phase II to establish the optimum concrete mixes incorporating RAP to be recommended. Concrete mixtures, with 0% to 40% RAP as aggregate replacement and using 20% fly ash and 50% slag as cement replacement, were designed using the optimized aggregate gradation (OAG) technique instead of the American Concrete Institute (ACI) method. Among the RAP concrete evaluated, the 20% RAP concrete mixes with 0%, 20% fly ash, and 50% slag as cement replacement were able to meet Florida Department of Transportation's (FDOT) over-design compressive strength of 29 MPa (4200 psi) at 28 days. Using 20% and 40% RAP in concrete could result in saving in the total cost of aggregate by 9% and 17%, respectively. When the RAP is not refined (e.g., no washing of RAP, and no separating of coarse and fine portions), it is recommended that 20% of RAP can be used as aggregate replacement in pavement concrete.

A high cementitious paste volume (CPV) can increase the early cracking tendency of the concrete and reduce the durability of concrete pavement. This study investigated the effects of minimized CPV in slipformed pavement concrete (SPC) with blended aggregates (BA). Based on the laboratory results, the performance of pavement concrete with different CPV was evaluated. The CPV of standard SPC can be reduced to 25.0% without affecting its properties as evaluated by compressive strength, drying shrinkage and surface resistivity tests However, the CPV of SPC with optimized aggregate gradation (OAG) using BA technique can be further reduced to 22.5% with satisfactory properties. The SPC mixes with OAG was noted to have better potential performance as a pavement concrete. SPC concrete using Portland limestone cement can give similar properties as those of the conventional concrete using ordinary Portland cement.

In Portland cement concrete, a high content of cementitious materials can cause early cracking. This study investigated the effects of minimised paste volume in structural concrete made with Portland limestone cement and blended aggregates (BA). The effects of using different types of cement and paste volumes were compared. It was found that concrete made using type IL cement (containing 14% limestone powder) showed comparable performance to concrete made with type I/II cement. Based on the results of laboratory testing and numerical modelling, the performance of concretes with different paste volumes was evaluated. The results showed that the paste volume could be reduced by around 27% without affecting the properties of the concrete. Using the BS technique, the paste volume could be further reduced by 24%. Concrete mixes prepared using the BA technique were found to have better potential performance than the reference concrete. It was concluded that the use of type IL cement and BA can effectively reduce the initial cost and carbon dioxide emissions of structural concrete without loss of performance.

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