Anal Kanti Mukhopadhyay

Activation Energy of Alkali-Silica Reaction and Dilatometer Method

Alkali-silica reaction (ASR) continues to be a detriment to the long-term performance of concrete. Certain initial conditions related to material alkalinity, aggregate reactivity, humidity, and temperature conditions are known to initiate ASR. A key factor in the prediction of ASR in concrete over time is the reactivity of the aggregate, but current test methodology is largely simulative in nature and yields mainly empirical results that apply to only a narrow band of conditions, and leave many questions as to whether these methods have any relevance to concrete performance under field conditions. Improvement can be found by using a performance-based approach that can address the ASR potential of concrete at levels of alkali, temperature, and moisture that are realistic and representative of actual field conditions. In the present study, the concept of ASR-related activation energy is introduced as a representative single parameter of the ASR. An attempt has been made to introduce the dilatometer test met...

Selection of Design Factors for the Use of Gravel in CRC Paving

Gravel aggregates have been used for many years in the construction of continuous reinforced concrete (CRC) pavements in Texas. However, these pavements are in many instances subject to delamination and spalling distresses, and thus costly to maintain and repair. Evidence collected from extensive field studies has indicated that the bond of aggregate-mortar interface at an early age is one of the most significant factors affecting the development of delamination and eventual spalling. In this research, a factional factorial design (the Taguchi method) was applied to investigate the methodology for improving delamination resistance of CRC pavements. Four factors (i.e., aggregate type, water/cementitious ratio, replacement of ultra-fine ash, and curing method) with three levels for each factor based on the orthogonal array were considered. A fracture mechanics parameter, fracture roughness, was used to represent the aggregate-mortar bond strength. The significances of each factor to achieve better fracture toughness were determined, and the optimum design combination was subsequently chosen and validated. The consistency between the results from the experimental design and laboratory validation provides highway agencies valuable recommendations and aid in selecting design factors for the use of gravel in paving construction to relieve delamination and further spalling distresses. A comprehensive investigation on overall aggregate contribution to pavement bonding performance will be considered in future research to ensure the integrity of the evaluation and analysis.

Evaluation of Alkali-Silica Reaction Potential of Aggregate Using Dilatometer Method

Existing test methodology for alkali silica reactivity (ASR) are applicable to only a narrow band of accelerated conditions and doubts remain whether these methods have any relevance to concrete performance under field conditions. Aggregate reactivity is a key factor in predicting the concrete ASR and is a function of alkalinity, temperature, size and crystallinity. Recently developed at the Texas Transportation Institute, Texas A&M University, a testing apparatus called a dilatometer has been used to measure aggregate ASR expansion and introducing activation energy as a single parameter to represent ASR reactivity. The expansion-time characteristics as a function of temperature can be expressed by the term activation energy (Ea). The rationality of the dilatometer test procedure is explored by conducting comprehensive laboratory experiments related to the effects of test solution (NaOH) alkalinity, temperature Ca(2+) contents on Ea. Dilatometer measures the volumetric expansion due to ASR and accounts the direct measurement of expansion produced by the reaction products. Based on the test results, it is observed that this test method will be useful to evaluate ASR potential of aggregates based on their Ea within a very short period of time (e.g., within 3 days). The dependency of Ea on alkalinity, Ca(2+) content and aggregate size provides a means to evaluate ASR potential of concrete relative to levels of alkali and temperature that occur under field conditions.