Ward R. Malisch Concrete Construction Symposium (Part 1)-After Two Hundred Years of Estimating Evaporation, It Is Still a Mystery (PDF)

After Two Hundred Years of Estimating Evaporation, It Is Still a Mystery (PDF)

Pdf Summary

The Concrete Convention and Exposition presents a compelling discussion on the complexities of estimating evaporation, particularly in relation to concrete. Despite 200 years of efforts, accurate evaporation prediction remains elusive. The event highlights the challenges associated with measuring evaporation rates from water-covered surfaces and concrete, noting significant errors when standardized measurement protocols aren't followed. The discussion emphasizes the importance of considering environmental 'evaporativity', akin to concepts like Wind-Chill or Heat Index, to better quantify conditions affecting evaporation.<br /><br />Key conclusions are drawn regarding the tools available for estimating evaporation rates, such as equations, nomographs, and digital applications. However, these tools often yield a 40% error margin for water surfaces and potentially 200% for concrete when deviating from prescribed measurement instructions. For reliable estimations, standardized protocols for temperature, relative humidity, and wind speed are necessary, alongside accounting for variable changes and result uncertainties. Additionally, the acceptance criteria should be based on bleed rate, which varies with the mixture, depth, consolidation, and time.<br /><br />The session underscores the significance of evaporation in concrete, as drying leads to reduced hydration, strength loss, and potential durability issues due to shrinkage, which causes tension-induced cracking. Evaporation rate estimates are influenced by factors such as temperature, vapor pressure, and wind speed, complicating accurate predictions. Historical models, like Dalton's Law and its subsequent applications, are scrutinized for their limitations, especially when the conditions deviate from established norms, such as the impact of solar radiation, which was not originally considered. <br /><br />The convention advocates for rigorous field testing and empirical constant adjustments to improve prediction models, emphasizing the need for continuous research and development to refine our understanding and management of evaporation in concrete applications.

Keywords

evaporation

concrete

measurement

environmental evaporativity

temperature

humidity

wind speed

hydration

cracking

prediction models