Journal of Materials in Civil Engineering

Optical spectroscopy is a viable approach for subsurface monitoring of pH levels in civil engineering materials. In this work, we describe a method by which optical fibers may be implemented as probes for the in situ measurement of pH levels. This paper describes the development of a nanoporous polymeric matrix, which hosts pH-sensitive chromoionophores. Details of how this pH indicator is strongly attached to the polymer chains through hydrogen bonds are described. Experiments are conducted in the laboratory in aqueous media for monitoring pH levels in highly alkaline and moderately acidic regions. Some detail on indicator immobilization, and signal reversibility are also reported.

When concrete is sprayed during shotcreting, inevitably some material is lost due to rebound. The relative losses for coarse aggregates and fibers are higher than that for the rest, and therefore the composition of the material in-place is deficient in these phases. In order to compensate for such loss and indeed to minimize it, one must identify the parameters affecting rebound and comprehend the underlying mechanisms. Recent work has established a theory of rebound for coarse aggregates. However, fibers differ from aggregates in their material and geometric properties and the effect of these must be understood in order to extend the existing theory of rebound to fibers. This is a study on the influence of particle density upon the rebound of a projectile impinging via the dry-mix process onto fresh shotcrete. The empirical model developed in this study postulates that a lower aggregate density favors lower rebound and this prediction was verified using two kinds of lightweight aggregates in dry-mix shotcrete.

The serviceability of concrete structures is a problem in which creep and damage are coupled. In this paper, we present experimental investigations on concrete that involve tertiary creep. We consider residual capacity tests on notched bending beams and investigate the evolution of size effect due to basic creep. In these experiments, beams are first subjected to a constant load, at a given ratio of the maximum capacity during $90\text{days}$ . They are then loaded up to failure and their residual capacity is obtained. During the creep phase, acoustic emission is analyzed and it shows that damage develops under creep. The comparison between the size effect test results with and without creep exhibits variations of the fracture properties of the material. The fracture energy and the size of the fracture process zone decrease when creep occurs prior to failure. These results, which include size effect fracture tests, may serve for the development and validation of coupled creep-damage models.

The current method of determining the moisture susceptibility of asphalt concrete mixtures is American Association of State Highway and Transportation Officials (AASHTO) T283. AASHTO T283 is based on the Marshall mix design method, however the current state of the practice for an asphalt concrete mixture design is the Superpave mix design method. There has not been a transition in test procedure from Marshall mix design to Superpave mix design in that Superpave adopted AASHTO T283 to evaluate the moisture susceptibility of asphalt concrete mixtures even though it was based on Marshall mix design. The procedures in AASHTO T283 and National Cooperative Highway Research Program (NCHRP) Report 444 consider the loss of strength due to freeze/thaw cycling and the effects of moisture existing in specimens compared to unconditioned specimens. Current research (NCHRP Project 9-34) is considering the use of a modified environmental conditioning system (ECS) with dynamic complex modulus testing. However, mixtures do not experience such a pure phenomenon. Pavements undergo cycling of environmental conditions, but when moisture is present, there is repeated hydraulic loading with development of pore pressure in mixtures. Thus, AASHTO T283 and NCHRP Report 444 do not consider the effect of pore pressure, but rather consider a single load effect on environmentally conditioned specimens. The test procedure proposed in this paper uses a retained dynamic modulus of 60% of conditioned specimens to unconditioned specimens. This initial criterion was derived as it is the same percentage of mixtures that fail the AASHTO T283 criteria (80%) of the 21 field mixes that were sampled. Comparison of mixtures performance ranked via AASHTO T283 and the proposed retained dynamic modulus criteria results in considerably different rankings. Pavements undergo cycling of environmental conditions, but when moisture is present, there is repeated hydraulic loading with the development of pore pressure in mixtures. Thus, the results of this testing can be input into the AASHTO Mechanistic-Empirical Pavement Design Guide to consider the effects of unconditioned versus conditioned dynamic modulus values and their respective impacts in pavement performance in terms of predicting pavement distresses.

Different methods have been developed to assess fatigue cracking of asphalt mixtures based on dissipated energy. Most of these methods have been motivated by the need to develop a unified fatigue criterion that is independent of the mode of loading. This paper offers critical analyses of the energy methods based on their theoretical ability to: (1) unify the results from controlled-strain and controlled-stress modes of testing for the same material; and (2) accurately assess the fatigue cracking life of different materials. The efficacy of these methods is quantitatively compared using a common set of fatigue test data. The fatigue test data were obtained using the dynamic mechanical testing of three different mixtures that have been shown to exhibit different fatigue cracking resistance in the field.