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.

A laboratory and field testing program was conducted to evaluate the performance and usability of internally cured concrete (ICC) using lightweight aggregates for bridge decks and concrete pavement slabs under Florida conditions. The laboratory testing program evaluated three standard mixes (SM) and three corresponding ICC mixes with the same water-cementitious (w/c) ratios and cementitious materials contents. The ICC mixes were produced by replacing a part of the fine aggregate with a pre-wetted lightweight aggregate (LWA). The quantity of LWA used was an amount that would supply 7 lb of absorbed water per 100 lb of cementitious materials used. The amounts of water-reducing admixtures needed for the ICC mixes to achieve the same workability of the fresh concrete were less than those for the standard mixes with the same w/c ratios. The compressive strength, flexural strength, elastic modulus, splitting tensile strength, and coefficient of thermal expansion of the ICC mixes were lower than those of the standard mixes with the same w/c ratio. The ICC mixes showed substantially greater resistance to shrinkage cracking than the standard mixes as observed from the results of the restrained shrinkage ring test. Two ICC test slabs and one SM test slab were constructed to evaluate the performance of ICC in pavement slabs. The results of the critical stress analysis showed that at a critical loading condition, the computed stress-tostrength ratios for the ICC slabs were lower than that for the SM slab. Visual inspection of the SM slab after heavy vehicle simulator (HVS) loading showed that some hairline cracks could be seen next to the wheel path. These hairline cracks could be caused when micro shrinkage cracks developed into hairline cracks after the slab was loaded repetitively by the HVS wheel load. No visible cracks were observed from the two ICC test slabs. Based on the results of the critical stress analysis and the visual inspection of the three test slabs, the ICC test slabs appeared to have better performance than the standard-mix slab. A field testing program to further assess the performance and benefits of ICC mixes in bridge deck and pavement applications is recommended.

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