Investigation Into Pavement Curing Materials and Surface Concrete Properties


Book Description

Appropriate curing is important for concrete to achieve the designed properties. At present, spraying liquid membrane-forming curing compound is the most common method used in pavement and other concrete structure construction. Although a great deal of work has been done on concrete curing, most studies have focused on the effects of curing conditions (such as temperature and relative humidity) on concrete properties (such as strength and freeze/thaw durability). Limited research has been done to study different curing compounds and the changes in the surface concrete properties induced by different curing compounds and applications technologies. The present research was conducted to evaluate curing compounds, application technologies, and their effects on concrete properties, especially on the surface concrete properties. Three curing compounds were selected and applied to concrete (mortars and pastes) at three different times after casting. Two application methods, single and double layer applications, were employed. Moisture content, conductivity, sorptivity, and degree of hydration were measured at different depths in the specimens. Flexural and compressive strength of the specimens were also tested. Statistical analysis was conducted to examine the relationships between these properties. It was found, in this project, that the application of curing compound improved the concrete properties. The application of the high-efficiency-index curing compound gave better properties than the low-efficiency-index curing compound. Compared with other test methods in this project, the sorptivity test was the most sensitive test, which gave difference for different curing conditions.




A New Protocol for Evaluating Concrete Curing Effectiveness


Book Description

Excessive early-age concrete surface moisture evaporation causes many problems of concrete pavements, such as plastic shrinkage cracking and delamination; the use of liquid membrane-forming curing compounds is one of the most prevalent methods to mitigate the issues. However, the present standard test, ASTM C 156-98, "Standard Test Method of Water Retention by Concrete Curing Materials" has some inherent limitations in assessing the curing effectiveness of concrete. To better apply curing practices and qualify the curing compound, a new evaluation protocol is introduced in this study. The new protocol consists of using measured relative humidity and temperature to calculate an effectiveness index (EI) which serves as an indicator of the effectiveness of curing. Moistures loss and surface abrasion resistance measurements were made on concrete specimen, and were found to have significant correlation with EI, where higher EI were associated with lower moisture loss and higher surface abrasion resistance. EI was also found to be sensitive to ambient wind condition, types of curing compound and the application rate of the curing compound. Dielectric constant (DC) measurements were also made on concrete specimens indicating the free moisture content on the surface concrete. The DC measurements were also found to differentiate the quality of curing under different ambient conditions, with various types of the curing compounds and the w/c of the concrete mixture. The utility of using the new protocol to assess concrete curing compound effectiveness was also evaluated under the field condition. Both EI and DC measurements showed potentials to distinguish the curing quality for concrete pavement construction. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151295




Investigation Into Improved Pavement Curing Materials and Techniques


Book Description

Concrete curing is closely related to cement hydration, microstructure development, and concrete performance. Application of a liquid membrane-forming curing compound is among the most widely used curing methods for concrete pavements and bridge decks. Curing compounds are economical, easy to apply, and maintenance free. However, limited research has been done to investigate the effectiveness of different curing compounds and their application technologies. No reliable standard testing method is available to evaluate the effectiveness of curing, especially of the field concrete curing. The present research investigates the effects of curing compound materials and application technologies on concrete properties, especially on the properties of surface concrete. This report presents a literature review of curing technology, with an emphasis on curing compounds, and the experimental results from the first part of this research-lab investigation. In the lab investigation, three curing compounds were selected and applied to mortar specimens at three different times after casting. Two application methods, single- and double-layer applications, were employed. Moisture content, conductivity, sorptivity, and degree of hydration were measured at different depths of the specimens. Flexural and compressive strength of the specimens were also tested. Statistical analysis was conducted to examine the relationships between these material properties. The research results indicate that application of a curing compound significantly increased moisture content and degree of cement hydration and reduced sorptivity of the near-surface-area concrete. For given concrete materials and mix proportions, optimal application time of curing compounds depended primarily upon the weather condition. If a sufficient amount of a high-efficiency-index curing compound was uniformly applied, no double-layer application was necessary. Among all test methods applied, the sorptivity test is the most sensitive one to provide good indication for the subtle changes in microstructure of the near-surface-area concrete caused by different curing materials and application methods. Sorptivity measurement has a close relation with moisture content and degree of hydration. The research results have established a baseline for and provided insight into the further development of testing procedures for evaluation of curing compounds in field. Recommendations are provided for further field study.




The effectiveness of membrane curing compounds for portland cement concrete pavements


Book Description

Membrane curing compounds are widely used to cure concrete in highway construction. The function of these compounds is to form a membrane that helps retain moisture in the concrete slab, otherwise lost through evaporation. The amount of evaporation loss varies as a function of the environmental conditions and the temperature of the concrete mass during the curing period. This rpeort provides an evaluation of the performance of membrane curing compounds as related to concrete material properties such as tensile and flexural strength, stiffness, surface durability, and density. In addition to traditional testing methods, the non-destructive, in-situ, Spectral Analysis of Surface Waves method is also used to observe and measure material properties as a function of time. Testing can start at initial set or when the modulus of elasticity for concrete is about 10,000 psi.




Standard Practice for Concrete


Book Description







Evaluation and Enhancement of Curing Efficiency of Joints in Concrete Pavements


Book Description

Optimum curing is essential in controlling durability performance of concrete. Absorption has been used as an indicator for quantifying the concrete durability, while the reliability of current absorption test methods with respect to curing efficiency and geometry of joints in concrete pavements is still unexplored. Curing efficiency of joints at early-age may be compromised due to uncontrolled evaporation resulting from saw-cutting processes. Therefore, providing an optimum curing and monitoring its efficiency with a real-time continuous measure is appealing. Also, a quantitative model of unsaturated flow ingress with respect to curing applications may provide a holistic understanding to predict the concrete durability. Therefore, this thesis aimed at assessing the effect of different curing compound applications on concrete pavements and overfilling joints with curing compound immediately after saw-cutting on improving the quality of concrete microstructure. Also, an effort was made to develop a customized test protocol for determining the absorption capacity of joints in concrete pavements. In addition, this thesis explored the correlation between the dielectric response of real-time sensor embedded in concrete with hydration development of paste as well as setting time. Moreover, this thesis investigated and developed an analytical model based on Katz-Thompson relationship to determine the absorption capacity of joints in concrete pavements according to an absorption test customized to the joint geometry of pavements. This thesis program involved experiments on laboratory specimens as well as cores extracted from field pavement and laboratory slabs. Absorption, rapid chloride penetrability, maturity, thermogravimetry, mercury intrusion porosimetry, and scanning electron microscopy tests were conducted. The results indicated applying a thorough coat and overfilling the joints with curing compound immediately after saw-cutting significantly improved concrete microstructure. Also, the proposed absorption protocol was efficient, robust and reliable in reflecting concrete microstructure of field pavement sections. Moreover, the dielectric response of concrete is strongly correlated to the hardening threshold and strength/hydration development of concrete, and thus it may be potentially used as a field indicator. Finally, the unsaturated flow model reliably simulated fluid transport at joint locations in concrete with accurate predictions relative to experimental results.







An Introduction to Advanced Issues in Curing Portland Cement Concrete Pavement


Book Description

Technical guidance for civil engineers and others interested in advanced technology issues regarding curing portland cement concrete pavement for streets and highways. Here is what is discussed: 1. INTRODUCTION 2. BLEEDING RATE—EVAPORATION RATE RELATIONSHIP 3. EFFECTIVENESS OF EVAPORATION REDUCERS 4. TIME OF CURING COMPOUND APPLICATION 5. WATER-RETENTION REQUIREMENTS FOR CURING COMPOUNDS 6. VARIABILITY IN TEST METHOD FOR WATER RETENTION OF CURING COMPOUNDS—ASTM C 156 7. APPLICATION RATE OF CURING COMPOUNDS 8. RECOVERY FROM POOR OR LATE APPLICATION OF CURING COMPOUND 9. EFFECT OF CLIMATIC CONDITIONS ON CURING COMPOUND DRYING TIME 10. APPLICATION OF CURING COMPOUND TO TINED SURFACES—EFFECT OF SAGGING 11. TEST METHODS FOR MEASURING CURING COMPOUND APPLICATION 12. LENGTH OF CURING 13. TEST METHODS FOR MEASURING CURING EFFECTIVENESS 14. THERMAL STRESS DUE TO EVAPORATIVE COOLING 15. CONCLUSIONS AND RECOMMENDATIONS.