Investigation into Improved Pavement Curing Materials and Techniques: Part 2 - Phase III, March 2003

Appropriate curing is important for concrete to obtain the designed properties. This research was conducted to evaluate the curing effects of different curing materials and methods on pavement properties. At present the sprayed curing compound is a common used method for pavement and other concrete structure construction. Three curing compounds were selected for testing. Two different application rates were employed for the white-pigmented liquid curing compounds. The concrete properties of temperature, moisture content, conductivity, and permeability were examined at several test locations. It was found, in this project, that the concrete properties varied with the depth. Of the tests conducted (maturity, sorptivity, permeability, and conductivity), conductivity appears to be the best method to evaluate the curing effects in the field and bears potential for field application. The results indicated that currently approved curing materials in Iowa, when spread uniformly in a single or double application, provide adequate curing protection and meet the goals of the Iowa Department of Transportation. Experimental curing methods can be compared to this method through the use of conductivity testing to determine their application in the field.

Investgiation into Improved Pavement Curing Materials and Techniques: Part 1 - Phases I and II, April 2002

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.

Improving Concrete Pavement Curing, March 2003

· Evaluate the effect of different curing materials and techniques on concrete pavement properties. · Better understand the relationships between various concrete test measurements and concrete properties affected by curing.

Deicer Scaling Resistance of Concrete Mixtures Containing Slag Cement Phase 2: Evaluation of Different Laboratory Scaling Test Methods, TPF-5(100), 2012

With the use of supplementary cementing materials (SCMs) in concrete mixtures, salt scaling tests such as ASTM C672 have been found to be overly aggressive and do correlate well with field scaling performance. The reasons for this are thought to be because at high replacement levels, SCM mixtures can take longer to set and to develop their properties: neither of these factors is taken into account in the standard laboratory finishing and curing procedures. As a result, these variables were studied as well as a modified scaling test, based on the Quebec BNQ scaling test that had shown promise in other research. The experimental research focused on the evaluation of three scaling resistance tests, including the ASTM C672 test with normal curing as well as an accelerated curing regime used by VDOT for ASTM C1202 rapid chloride permeability tests and now included as an option in ASTM C1202. As well, several variations on the proposed draft ASTM WK9367 deicer scaling resistance test, based on the Quebec Ministry of Transportation BNQ test method, were evaluated for concretes containing varying amounts of slag cement. A total of 16 concrete mixtures were studied using both high alkali cement and low alkali cement, Grade 100 slag and Grade 120 slag with 0, 20, 35 and 50 percent slag replacement by mass of total cementing materials. Vinsol resin was used as the primary air entrainer and Micro Air® was used in two replicate mixes for comparison. Based on the results of this study, a draft alternative test method to ASTM C762 is proposed.

Bridge Deck Repair Using Epoxy Resin, HR-177, 1979

Research funds were approved for the purchase of equipment designed to proportion and inject epoxy resins into delaminated areas of bridge decks. Through investigation and refining of this process, it was anticipated that a maintenance procedure would be developed to delay spalling of bridge decks by "gluing down" delaminated areas before spalling occurred.

Blanket Curing to Promote Early Strength Concrete, MLR-87-7, 1989

Fast Track concrete has proven to be successful in obtaining high early strengths. This benefit does not come without cost. Special Type III cement and insulating blankets to accelerate the cure add to its expense when compared to conventional paving. This research was intended to determine the benefit derived from the use of insulating blankets to accelerate strength gain in three concrete mixes using Type I cement. The goal was to determine mixes and curing procedures that would result in a range of opening times. This determination would allow the most economical design for a particular project by tailoring it to a specific time restraint. Three mixes of various cement content were tested in the field. Flexural beams were cast for each mix and tested at various ages. Two test sections were placed for each mix, one section being cured with the addition of insulating blankets and the other being cured with only conventional curing compound. Iowa Department of Transportation specifications require 500 psi flexural strength before a pavement can be opened to traffic. Concrete with Fast Track proportions (nominal 7 1/2 bag), Type I cement, and insulating blankets reached that strength in approximately 36 hr, a standard mix (nominal 6 1/2 bag) using the blankets in approximately 48 hr, and the Fast Track proportions with Type I cement without blankets in about 60 hr. The results showed a significant improvement in early strength gain with the use of insulating blankets.

Investigation of the Loss of Prestress in Prestressed Concrete Beams due to Steam Curing, HR-62, 1961

Mass production of prestressed concrete beams is facilitated by the accelerated curing of the concrete. The ·method most commonly used for this purpose is steam curing at atmospheric pressure. This requires concrete temperatures as high as 150°F. during the curing period. Prestressing facilities in Iowa are located out of doors. This means that during the winter season the forms are set and the steel cables are stressed at temperatures as low as 0°F. The thermal expansion of the prestressing cables should result in a reduction of the stress which was placed in them at the lower temperature. If the stress is reduced in the cables, then the amount of prestress ultimately transferred to the concrete may be less than the amount for which the beam was designed. Research project HR-62 was undertaken to measure and explain the difference between the initial stress placed in the cables and the actual stress which is eventually transferred to the concrete. The project was assigned to the Materials Department Laboratory under the general supervision of the Testing Engineer, Mr. James W. Johnson. A small stress bed complete with steam curing facilities was set up in the laboratory, and prestressed concrete beams were fabricated under closely controlled conditions. Measurements were made to determine the initial stress in the steel and the final stress in the concrete. The results of these tests indicate that there is a general loss of prestressing force in excess of that caused by elastic shortening of the concrete. The exact amount of the loss and the identification of the factors involved could not be determined from this limited investigation.

Effect of Grooved Concrete on Curing Efficiency, MLR-83-4, 1983

The textured concrete surface on all PCC primary paving projects (and when specified on secondary projects) is required to be grooved in a specified manner. The laboratory test for determining the efficiency index of concrete curing compounds is made on slabs that are not grooved. This short investigation was undertaken to determine any changes in the curing efficiency index when using various rates of application of curing compound on grooved concrete. Currently a 95 percent curing efficiency index is specified at an application rate of 15 square yards per gallon. Can this efficiency be achieved, and if so at what application rate, on grooved concrete? Grooving the concrete greatly increases the surface area and also causes the liquid curing compound to run off the high spots and collect in the grooves.

Durability of P.C. Concrete as Affected by Aggregate Size, Curing and Proportions, R-214, 1968

The durability of concrete is a most important aspect in pavement life. Deterioration of the interstate portland cement concrete pavement has prompted various studies of factors which may contribute to the durability. Studies of cores taken from deteriorated areas indicated that the larger particles of coarse aggregate may contribute greatly to the problem. This indication was mainly due to the analysis of the cracking pattern which showed that most of the cracks passed through the larger aggregates and the larger aggregate particles were more cracked than the smaller particles. The purpose of this project is to determine if the size of the coarse aggregate has a bearing on the durability of freeze and thaw beams. A secondary purpose of this project is to determine what effect the method of curing and proportions have on the durability of freeze and thaw beams.

Steam Curing of Portland Cement Concrete at Atmospheric Pressure, HR-40, 1962

The primary reason for using steam in the curing of concrete is to produce a high early strength. This high early strength is very desirable to the manufacturers of precast and prestressed concrete units, which often require expensive forms or stress beds. They want to remove the forms and move the units to storage yards as soon as possible. The minimum time between casting and moving the units is usually governed by the strength of the concrete. Steam curing accelerates the gain in strength at early ages, but the uncontrolled use of steam may seriously affect the growth in strength at later ages. The research described in this report was prompted by the need to establish realistic controls and specifications for the steam curing of pretensioned, prestressed concrete bridge beams and concrete culvert pipe manufactured in central plants. The complete project encompasses a series of laboratory and field investigations conducted over a period of approximately three years.

A Study of Curing Methods and Type II Cements on the Durability of Concrete, R-11-Z(1), 1969

A program of A (90 day moist room), B (14 day moist room) and C (7 day moist room and 7 day 50%_humidity) type curing for the R-11-Z program of durability of concrete using the automatic freeze and thaw machine (ASTM C-291) has been used in the Materials Department of the Iowa State Highway Commission since December 6, 1966. A summary of the results obtained from then until March 25, 1968, indicates that the B and C type curing are yielding very little valuable information. However, the A cure exhibits a wide range of durability factors and also groups the aggregates in an order which is related to the service record (there are definite exceptions. The biggest disadvantage to the A cure is the length of time that it takes to complete the test (90 day cure and 38 day test). The Kansas Highway Department has experimented with different cements and aggregates in order to determine which combination offers a concrete with the best durability factor possible. In an experimental test section of highway, concrete made with a Type II cement appeared to have better durability than others made with Type I cements. Because of this, a question has been raised at the Iowa State Highway Commission - Can concrete made with Type II cements, because of a lesser amount of tricalcium aluminate, yield better durability than concrete made with Type I cements?

Impacts of Internal Curing on Concrete Properties, TR-676, 2015

Conventional concrete is typically cured using external methods. External curing prevents drying of the surface, allows the mixture to stay warm and moist, and results in continued cement hydration (Taylor 2014). Internal curing is a relatively recent technique that has been developed to prolong cement hydration by providing internal water reservoirs in a concrete mixture that do not adversely affect the concrete mixture’s fresh or hardened physical properties. Internal curing grew out of the need for more durable structural concretes that were resistant to shrinkage cracking. Joint spacing for concrete overlays can be increased if slab warping is reduced or eliminated. One of the most promising potential benefits from using internal curing for concrete overlays, then, is the reduced number of joints due to increased joint spacing (Wei and Hansen 2008).

Portland Cement Concrete Curing Compound Performance Phase I and Phase II, MLR-02-03, 2003

Testing the efficiency of Portland Cement Concrete (PCC) curing compounds is currently done following Test Method Iowa 901-D, May 2002. Concrete test specimens are prepared from mortar materials and are wet cured 5 hours before the curing compound is applied. All brands of curing compound submitted to the Iowa Department of Transportation are laboratory tested for comparative performance under the same test conditions. These conditions are different than field PCC paving conditions. Phase I tests followed Test Method Iowa 901-D, but modified the application amounts of the curing compound. Test results showed that the application of two coats of one-half thickness each increased efficiency compared to one full thickness coat. Phase II tests also used the modified application amounts, used a concrete mix (instead of a mortar mix) and applied curing compound a few minutes after molding. Measurements of losses, during spraying of the curing compound, were noted and were found to be significant. Test results showed that application amounts, testing techniques, concrete specimen mix design and spray losses do influence the curing compound efficiency. The significance of the spray losses indicates that the conventional test method being used (Iowa 901 D) should be revised.

Examination of Curing Criteria for Cold In-Place Recycling, TR-553, 2008

Cold In-Place Recycling (CIR) has been used widely in rehabilitating the rural highways because it improves a long-term pavement performance. A CIR layer is normally covered by a hot mix asphalt (HMA) overlay in order to protect it from water ingress and traffic abrasion and obtain the required pavement structure and texture. Curing is the term currently used for the period of time that a CIR layer should remain exposed to drying conditions before an HMA overlay is placed. The industry standard for curing time is 10 days to 14 days or a maximum moisture content of 1.5 percent, which appear to be very conservative. When the exposed CIR layer is required to carry traffic for many weeks before the wearing surface is placed, it increases the risk of a premature failure in both CIR layer and overlay. This study was performed to explore technically sound ways to identify minimum in-place CIR properties necessary to permit placement of the HMA overlay. To represent the curing process of CIR pavement in the field construction, three different laboratory curing procedures were examined: 1) uncovered, 2) semi-covered and 3) covered specimens. The indirect tensile strength of specimens in all three curing conditions did not increase during an early stage of curing but increased during a later stage of curing usually when the moisture content falls below 1.5%. Dynamic modulus and flow number increased as curing time increased and moisture contents decreased. For the same curing time, CIR-foam specimens exhibited the higher tensile strength and less moisture content than CIR-emulsion. The laboratory test results concluded that the method of curing temperature and length of the curing period significantly affect the properties of the CIR mixtures. The moisture loss index was developed to predict the moisture condition in the field and, in the future, this index be calibrated with the measurements of temperature and moisture of a CIR layer in the field.

Examination of Curing Criteria for Cold In-Place Recycling Phase 2: Measuring Temperature, Moisture, Deflection and Distress from CIR Test Section, TR-590, 2009

The previous research performed laboratory experiments to measure the impacts of the curing on the indirect tensile strength of both CIR-foam and CIR-emulsion mixtures. However, a fundamental question was raised during the previous research regarding a relationship between the field moisture content and the laboratory moisture content. Therefore, during this research, both temperature and moisture conditions were measured in the field by embedding the sensors at a midpoint and a bottom of the CIR layer. The main objectives of the research are to: (1) measure the moisture levels throughout a CIR layer and (2) develop a moisture loss index to determine the optimum curing time of CIR layer before HMA overlay. To develop a set of moisture loss indices, the moisture contents and temperatures of CIR-foam and CIR-emulsion layers were monitored for five months. Based on the limited field experiment, the following conclusions are derived: 1. The moisture content of the CIR layer can be monitored accurately using the capacitance type moisture sensor. 2. The moisture loss index for CIR layers is a viable tool in determining the optimum timing for an overlay without measuring actual moisture contents. 3. The modulus back-calculated based on the deflection measured by FWD seemed to be in a good agreement with the stiffness measured by geo-gauge. 4. The geo-gauge should be considered for measuring the stiffness of CIR layer that can be used to determine the timing of an overlay. 5. The stiffness of CIR-foam layer increased as a curing time increased and it seemed to be more influenced by a temperature than moisture content. The developed sets of moisture loss indices based on the field measurements will help pavement engineers determine an optimum timing of an overlay without continually measuring moisture conditions in the field using a nuclear gauge.