A compressive laboratory testing program, field testing program, numerical analysis, and life-cycle cost analysis were conducted to evaluate the beneficial effects of incorporating shrinkage-reducing admixture (SRA), polymeric microfibers (PMF), and optimized aggregate gradation (OAG) into an internally cured concrete (ICC) mix for rigid pavement application. Results from the laboratory program indicate that all ICC mixes outperformed the standard concrete (SC) mix. All ICC mixes showed a decrease in drying shrinkage compared to the SC mix. Based on the laboratory program, three ICC mixes and one of the SC mixes were selected for the full-scale test subjected to a heavy vehicle simulator for accelerated fatigue testing. Extensive testing and analysis have shown that ICC mixes incorporating SRA, PMF, and OAG can be beneficially used in pavement applications to achieve increased pavement life.

In this study, a procedure for interpreting impact-echo data in an automated, simple manner for detecting defects in concrete bridge decks is presented. Such a procedure is needed because it can be challenging for inexperienced impact-echo users to correctly distinguish between sound and defective concrete. This data interpretation procedure was developed considering the statistical nature of impact-echo data in a manner to allow impact-echo users of all skill levels to understand and implement the procedure. The developed method predominantly relies on conducting segmented linear regression analysis of the cumulative probabilities of an impact-echo data set to identify frequency thresholds distinguishing sound concrete from defective concrete. The accuracy of this method was validated using two case studies of five slab specimens and a full-scale bridge deck, each containing various typical defects. The developed procedure was found to be able to predict the condition of the slab specimens containing shallow delaminations without human assistance within 3.1 percentage points of the maximum attainable accuracy. It was also able to correctly predict the condition of the full-scale bridge deck containing delaminations, voids, corrosion damage, concrete deterioration, and poorly constructed concrete within 3.5 percentage points of the maximum attainable accuracy.

Beam specimens of polypropylene fiber-reinforced concrete (PPFRC) with 1.3 vol. % having three different sizes, 100 x 100 x 400 mm, 150 x 150 x 530 mm, and 200 x 200 x 650 mm, were tested under four-point bending tests to investigate the flexural behavior (flexural and post-cracking strengths). The beam specimens were quarried from PPFRC slabs to evaluate the influence of the fiber orientation and distribution and the concrete casting and loading directions on the flexural behavior. The test results show that the difference in the fabrication methods of specimens considerably affected the flexural behavior. The flexural cracking strength was accompanied by the size effect and the post-cracking strength, significantly decreased when compared with standardized prism specimens; however, the post-cracking strength was not sensitive to the size effect. Furthermore, the pavement thickness of PPFRC was compared with that of plain concrete with the calculation using the post-cracking strength.

The use of blended cements enables the production of concretes with low embodied carbon and improved resistance to chloride penetration compared to general-purpose (GP) cement concrete. This paper reports the chloride diffusion characteristics in terms of the apparent diffusion coefficient (Da), surface chloride concentration (Cs), and corresponding aging factors (a and b) of low-carbon concrete (LCC) derived from up to 9-year long-term exposure of small reinforced concrete slabs in both laboratory-simulated and field marine tidal conditions. LCC with either 30% fly ash or 50% slag provides slightly to significantly lower 28-day compressive strength than GP cement concrete at the same water-binder ratio but significantly better resistance to chloride penetration. The long-term chloride profile necessary to determine the concrete cover where the chloride threshold is reached can be determined with the Da.t0, Cs.t0, and corresponding age factors a and b, where t0 is the 1-year time of exposure. The improved resistance to chloride penetration by the use of fly ash and slag as cement replacements was largely due to their intrinsic influence on the microstructure of the concrete. The results highlight that the difference in chloride penetration arises from the change in test methods, thus the importance of calibration when data obtained from laboratory concrete were used as inputs for service-life design.

To control cracking of mass concrete slabs in nuclear power plants (NPPs), a dynamic curing technique is proposed based on the stress superposition principle and elastic assumptions. It optimizes the stress field through targeted regulation of temperature variation according to the measured elastic strain εem by flexible application of surface-protection techniques. The limit tensile strain of εem is defined as 120 με to guarantee no cracks would occur. In its application on two slabs, only one hairline vertical crack was observed when εem reached 130 με on the 12th day after casting. However, the tensile strain gradually decreased, and the crack tended to close with age. The presented technique has been verified on more than 20 NPPs throughout the continuous casting stage (and even the operation period), saving construction time in the meantime. In addition, it provides theoretical and technical guidance for further investigation of mass concrete with complicated cross-section shapes.