Jung Heum Yeon

Effect of Relative Humidity on Coefficient of Thermal Expansion of Hardened Cement Paste and Concrete

The coefficient of thermal expansion (CTE) of concrete has substantial effects on the behavior and performance of portland cement concrete (PCC) pavement. The CTE is one of the input variables with significant effects on PCC pavement performance in the newly developed Mechanistic–Empirical Pavement Design Guide. Currently, the most advanced and accepted evaluation method for the CTE is the provisional AASHTO TP60. In this test method, concrete specimens are saturated before and during the testing. It has been recognized that the CTE of cement paste is influenced by the relative humidity (RH) within the specimen. Results from previous research studies were nearly consistent: the maximum CTE value occurs at about 70% RH and its value is almost twice the value at 100% RH. Laboratory evaluations were conducted to quantify the effects of RH on CTEs in cement paste and concrete. In the testing program, target RH levels within the specimens were 45%, 60%, 70%, 80%, and 100%. RH sensors were installed within the specimens during their preparation. The specimens were fabricated and cured in 23°C (73°F) and 50% RH conditions for 6 weeks. Subsequently, the specimens were placed in the environmental chamber until the internal RH values reached the target RH levels. Then CTE testing was conducted by changing temperatures while evaluating displacements with externally mounted vibrating wire gauges. The results showed some effects of RH on the CTE of cement paste and concrete, with maximum values at about 70% to 80% RH. The effect was larger for cement paste than for concrete. Considering the small effects of RH on the concrete CTE, AASHTO TP60 appears to provide adequate CTE values for PCC pavement analysis for environmental stresses.

Effects of Creep and Built-In Curling on Stress Development of Portland Cement Concrete Pavement under Environmental Loadings

An adequate evaluation of stress developments in concrete is essential to ensure well-performing and long-lasting portland cement concrete (PCC) pavement designs and construction. In this study, the effects of creep and built-in curling (BIC) on the stress history of PCC pavements under environmental loadings were investigated primarily through a series of field tests and numerical data interpretations. To identify the stress-dependent strain component within the in situ measured total strain, a nonstress cylinder (NC) was employed in the field tests. The identified stress-dependent strains from the field tests were converted to stresses using a step-by-step numerical method. To investigate the effect of creep on stress developments, stress histories were computed in two different ways—one with elastic analysis and the other with viscoelastic analysis—and then their difference (stress relaxation) over time was evaluated. The finding indicated that creep may be a key element in the evaluation of long-term stresses and, in turn, the design and analysis of PCC pavements. Furthermore, this study examined the impacts of BIC on the residual stresses of PCC pavements. The result showed that BIC may affect the early-age stress development, but it has little influence on the long-term environmental stress state.

Strength Development Characteristics and Economic Efficiency of Low Temperature Cured Acrylic Polymer Concrete: The Effect of Additive Type

This paper presents the strength development characteristics and the economic efficiency of low temperature cured acrylic polymer concrete containing different types of additives. In this study, two separate cases were mainly investigated: (1) when only MAA (polar monomer) was used as an additive and (2) when silane (coupling agent) in combination with TMPTMA (cross-linking agent) was used as an additive. The experimental results showed that compressive strength of over 80 MPa could be obtained in both cases even in low curing temperatures (i.e., 0 and -20°C). Also, the result of economic efficiency analysis showed that the use of MAA yielded a 10% less material cost than the use of TMPTMA and silane. This finding indicates that the use of MAA can be more beneficial from an economic perspective.

Remodeling of Deteriorated Irrigation Aqueducts Using Precast Polymer Concrete Flume

This study is designed to review the causes and modes of deterioration in irrigation aqueducts constructed with reinforced concrete, and introduce existing rehabilitation and new remodeling methods. As a result, because of the typical nature of irrigation aqueducts that are exposed to severe natural environment, the causes and modes of deterioration were more complex and diverse than other concrete structures. Also, due to the thinner cross sectional thickness of the structure, conducting a rehabilitation work was turned out to be difficult. As an active method for settling this problem, this study developed a method to remove the entire flume, upper structure of aqueduct, and replace with a precast flume constructed with polymer concrete. A loading test was performed using full-scale specimens, and then the suggested remodeling method was implemented in the actual field structures. The investigation showed that the suggested remodeling method was appropriate to secure the sustainability.