Dan G Zollinger

Evaluation of modified ASTM C 1260 accelerated mortar bar test for alkali-silica reactivity

Abstract Among the numerous tests prescribed for assessing alkali–silica reactivity, ASTM C 1260 has become the preferred test method because of rapidity of the test procedure. However, a general concern about this method is the severity of the test conditions. The authors have evaluated the functionality of the method after modifying some of the important test parameters such as water–cement ratio, normality of test solution, length of test period, and curing. Combinations of high- and low-alkali cement with and without Classes C and F fly ash were included in the test program. The results are presented in this paper.

Alkali-Silica Reactivity Potential of Aggregate and Concrete Evaluated by Dilatometer Method: Performance-Based Approach

Undesirable expansion of concrete due to a reaction between alkalis and certain type of reactive siliceous aggregates known as alkali-silica reactivity (ASR) continues as a major problem worldwide. Renewed interest in minimizing distress resulting from ASR emphasizes the need to develop predictable modeling of concrete ASR behavior under field conditions. Current test methods are either incapable of that or need long testing periods, which offer only limited predictive estimates of ASR behavior in a narrow band of field conditions. Therefore, an attempt was made to formulate a robust performance approach based on basic aggregate and concrete ASR material properties derived from dilatometry and a kinetic-based mathematical expression for ASR behavior. Since ASR is largely an alkali as well as a thermally activated process, the use of rate theory (Arrhenius relationship between temperature and alkali solution concentration) on the dilatometer time-expansion relationship provides a fundamental aggregate ASR material property known as activation energy. Activation energy is an indicator of aggregate reactivity, which is a function of alkalinity, particle size, crystallinity, calcium concentration, and so on. The studied concrete ASR material properties represent combined effects of mixture-related properties (e.g., water-cementitious material ratio, porosity, presence of supplementary cementitious materials) and maturity. A performance-based approach provides direct accountability for various factors affecting ASR, such as aggregate reactivity, temperature, moisture, calcium concentration, solution alkalinity, and water-cementitious material ratio. From test results, it was determined that the proposed model provides a means to predict ASR expansion development in concrete.

Test Method and Model Development of Subbase Erosion for Concrete Pavement Design

The erosion of material beneath a concrete slab is an important performance-related factor. If applied to the selection of base materials, this factor can enhance the overall design process for concrete pavement systems. However, erosion of the subbase has not been included explicitly in analysis and design procedures because there is no well-accepted laboratory test or related erosion model suitable for design. Therefore, this paper focuses on advancing a simple laboratory test method to evaluate erodibility of a subbase material and then introducing and validating an erosion model that incorporates the results from the new laboratory test method. Erosion-related design procedures were reviewed relative to previous test methods. Erosion models were evaluated for their utility to characterize the erosion resistance of subbase materials. With this information, a new test configuration was devised; it used a rapid triaxial test and a Hamburg wheel-tracking device for evaluating erodibility in relation to the degree of stabilization, base type, and cement content. Test devices, procedures, and results are explained and summarized for application in mechanistic design processes. A proposed erosion model is validated by comparing erosion predictions to erosion results.

STRAIN AND AGE EFFECTS ON BEHAVIOR OF A CONCRETE PAVEMENT JOINT SEALANT MATERIAL

A one-part self-leveling silicone joint sealant material was experimentally investigated in the laboratory. It was found that strain and age had apparent effects on the relaxation modulus of the material. Relaxation tests were conducted under different strain levels. The test samples were exposed to ultraviolet radiation and moisture for artificial aging before testing. For this largely deformable material, finite strain formulas were used in analysis of experimental data. Strain and age effects were successfully normalized in the relaxation master curve by using the superposition principle. On the basis of the master curve, a material model of the generalized Maxwell model in parallel type was constructed. The real time was scaled to the reduced time by time-strain shift and time-age shift factors so as to characterize the strain and age effects. This model is mathematically simple and can be easily applied in finite element programs for concrete pavement joint analysis.

Punchout study for continuously reinforced concrete pavement containing reclaimed asphalt pavement using pavement ME models

ABSTRACT The restricted use of reclaimed asphalt pavement (RAP) in hot mix asphalt (HMA) motivates the use of RAP in portland cement concrete (PCC) as an aggregate replacement. The addition of RAP causes significant changes in PCCs properties, but little research has been done to investigate the impact of these changes on pavement performances. In this study, punchout performances of continuously reinforced concrete pavement (CRCP) made with PCC containing RAP (RAP-PCC) slabs were extensively assessed using existing models in the Pavement ME. Based on the results, the major drawback for using RAP in CRCP is the RAP-PCCs reduced modulus of rupture (MOR); the reduced MOR causes higher stress to strength ratio in the slab, which can lead to higher chances of fatigue. However, the RAP-PCC slab is anticipated to have tighter transverse cracks due to the reduction in modulus of elasticity. A decrease in crack width could potentially yield a higher transverse crack load transfer efficiency (LTE). The Pavement ME simulations indicate that the CRCP made with RAP-PCC, which has tighter cracks, can maintain a higher LTE for a much longer time and ultimately leads to a longer pavement service life compared to the plain CRCP.

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.