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

Abstract

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.

Internal Relative Humidity, Autogenous Shrinkage, and Strength of Cement Mortar Modified with Superabsorbent Polymers

“…Once the autogenous shrinkage and IRH tests were completed, the specimens were unwrapped and stored in a controlled environment of 20 ± 1 °C and 70% RH until the specimens achieve an IRH of 70 ± 5%, where the maximum CTE occurs [4,5,6]. The RH values at the time of CTE testing were: 69.29% for Plain, 75.07% for SAP A 0.4, 68.12% for SAP B 0.4, 74.25% for SAP C 0.4, 67.09% SAP D 0.2, 71.88% for SAP D 0.4, and 73.26% for SAP D 0.6.…”

“…For this reason, the internal drying is clearly distinguished from typical long-term drying triggered by “diffusion-evaporation” mechanisms under prolonged environmental exposure. The internal drying is also often termed self-desiccation, and this propensity consequently increases the water molecule-holding capacity at the meniscus between liquid water and vapor in capillary pores, reducing the internal relative humidity (IRH) of a cementitious material system [4,5,6,7]. The bulk strain caused by the IRH changes under sealed, isothermal, and stress-free conditions is referred to as autogenous shrinkage [2,3,7], which is considered a crucial factor in raising the probability of early-age non-structural cracking in modern concrete members.…”

Effect of Aggregate Mineralogy and Concrete Microstructure on Thermal Expansion and Strength Properties of Concrete

“…The CTE is directly influenced by the aggregate type and aggregate volume [6,[11][12][13], as well as internal moisture conditions [14][15][16] and cement paste [17]. The CTE has shown not to be significantly impacted by water-to-cement ratio [17] and concrete age [14,18].…”

Effect of materials and age on the coefficient of thermal expansion of concrete paving mixture

“…Neville (1996) showed that the CTEs of concrete increased when the concrete was cured in air. Yeon, Choi and Won (2009) also reported that the CTE of both cement paste and concrete mixture varied depending on the concrete relative humidity (RH), and the maximum CTE was observed at approximately 70-80% RH.…”