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




Early-age Concrete Temperature and Moisture Relative to Curing Effectiveness and Projected Effects on Selected Aspects of Slab Behavior


Book Description

Concrete curing has long been realized to be important to produce durable concrete. Curing compound is widely used to cure concrete in the field. The current curing membrane evaluation method ASTM C 156, however, is incapable of distinguishing the curing compound quality and guiding the curing practice in the field. A new laboratory curing membrane evaluation protocol is developed in this study. It has the ability to rank the quality of curing compound and guide curing practice in the field according to the field ambient weather conditions and the type of curing compound. A series of field tests were conducted to investigate the key factors that affect the curing effectiveness in the field conditions. A finite element program, temperature and moisture analysis for curing concrete (TMAC2), is updated to solve the coupled and nonlinear heat transfer and moisture transport problems in early-age concrete. Moisture capacity is induced into the TMAC2, which makes it unique to characterize the self-desiccation. A full scale concrete pavement test study was conducted at the FAA National Airport Pavement Test Facility (NAPTF) near Atlantic City, New Jersey. In this study, the material properties, i.e. thermal conductivity and moisture diffusivity, were backcalculated from field data. Thereafter, backcalculated material properties were used to forward-calculate the temperature and moisture histories of all other sections. High order shear deformable theory is used to model the concrete slab curling and warping behavior because of highly nonlinear temperature and moisture gradients. The maximum shear strain is obtained a couple of inches below the concrete slab. This might account for the occurrence of delamination.




Effectiveness of Membrane-Forming Curing Compounds for Curing Concrete


Book Description

A search was made for test methods to evaluate the effectiveness of curing concrete. Test methods that include water absorptivity (proposed ASTM test), capillary porosity, combined water, splitting tensile strength, and abrasion resistance were evaluated. Curing compounds having a wide range of water retention values and meeting the requirements of ASTM C 309-89 and CRD-C 300 were obtained for evaluation. A few curing compounds were prepared in the laboratory by diluting one of the CRD-C 300 curing compounds with the vehicle solvent furnished by the manufacturer to obtain curing compounds that would not meet the requirements of either specification. The water-absorptivity test and an abrasion test developed in the laboratory were used to determine the effectiveness of the different curing compounds for curing concrete. Curing compounds meeting the requirements of ASTM-C 309-89 were found to be as effective as curing compounds meeting the requirements of CRD-C 300 for curing concrete. Two of the curing compounds that did not meet the specification requirements were also found to be effective based on the water-absorptivity test method. The abrasion test shows promise as a test method for evaluating the effectiveness of curing and is less time consuming than the water-absorptivity test method. Keywords: Abrasion, Construction materials, Absorptivity, Membrane-forming curing compounds, Moisture retention, Portland cement concrete, Portland cement mortar. (JG).




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.







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.










Guide for Curing of Portland Cement Concrete Pavements


Book Description

Information on the current state of knowledge of curing hydraulic-cement concrete and on current curing practice was gathered by means of a literature review and a review of current standard guidance. From this information, a draft guide for curing hydraulic-cement concrete pavements was developed. Draft guidance was based around type of curing used (water added, water retention by sheet, or curing compound) and around temperature effects. As a result of review by the project technical advisory panel, additional information was gathered from existing sources on several subjects. Laboratory studies were conducted on topics for which information was needed but not currently available. The result of the investigation was a set of guidelines that focused particularly on attention to details of moisture retention and temperature immediately after placing (initial curing period) and on details of selection of materials for final curing and determining when to apply final curing. Test methods for evaluating application rate of curing compound and effectiveness of curing were also reported. A separate report (FHWA RD-02-099 Guide for Curing of Portland Cement Concrete Pavements, Volume I) has been written that captures the details of the recommended guidance. That report is intended to be the principal technology transfer medium.




Standard Practice for Concrete


Book Description