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theses

Porous concrete is becoming an attractive pavement solution due to its great performances in mitigating urban heat island (UHI) effect and managing storm water. As a heterogeneous material, the properties of cement-based porous concrete are complicated to quantify and hard to predict. This thesis focused on the evaluation of thermal properties and air void characteristics of porous concrete. The thermal properties of aggregates, cement pastes, and porous concretes were measured by transient plate method (TPS) and steady-state heat flow meter method, respectively. X-ray computed tomography (CT) technique was utilized and three-dimensional (3-D) pictures were treated to analyze the microscopic structure of air voids in porous concrete. The existing analytical models were employed to estimate thermal conductivity of pervious concretes and compared to experimental measurements. The tests results show that thermal conductivity and heat capacity of cement paste increases as water cement ratio increases. Meanwhile, for the same mix design, the thermal properties of different cement paste samples had few variations. However, the porous concrete is very heterogeneous and the same mix design cannot ensure the similar porosity; instead, significant variations of porosity were observed. The existing analytical results did not show satisfactory prediction results of thermal conductivity as compared to testing results. This indicates the existing models are not suitable to estimate the thermal conductivity of porous concrete. This is because the models ignore the complex microscopic structures of porous concrete. Based on the CT-scanned images, within the horizontal plane of cylindrical sample, slight differences of normalized projected lengths of air voids were observed in the orthogonal horizontal directions; while the normalized projected length of connected voids in vertical direction was found smaller than those in horizontal directions. The smaller aggregates tend to form the longer air void length in porous concrete. The curvatures of air voids for smaller aggregates are greater than that of larger aggregates. Meanwhile, within the same mix design, the curvature of air voids increases with the increasing of porosity. The porosity and aggregate size do not have significant influences on the ellipticity and tortuosity of air voids within porous concrete. However, with the increase of porosity, the air voids tend to have the greater equivalent diameter.

ETD_8467

M.S.

Includes bibliographical references

by Pengyu Xie

doi:10.7282/T3542RRR

ETD graduate

The author owns the copyright to this work.