Nancy Whiting

Effectiveness of portland cement concrete curing compounds

Many different spray-on compounds are available for curing concrete, including newer products that are intended to address the environmental concerns associated with high volatile organic compound (VOC) contents. A laboratory study was conducted to examine the effectiveness of different types of curing compounds in retaining water for hydration, promoting concrete strength, and reducing permeability, relative to classic curing techniques such as plastic sheeting and ponding and relative to the use of no curing treatment. Comparisons of moisture loss, compressive strength, permeability, and capillary porosity were made for samples representing three high-VOC curing compounds, three low-VOC curing compounds, water curing, and plastic-sheet curing, and for samples with no curing treatment after 3 days and 28 days of curing. The performance of the six compounds tested varied greatly, but none of the compounds performed as well as the samples cured with water or plastic sheeting. All compounds performed better than samples with no curing treatment.

Using Recycled Concrete as Aggregate in Concrete Pavements to Reduce Materials Cost

The main objective of this project was to evaluate the effects of using aggregate produced from crushed concrete pavement as a replacement for natural (virgin) coarse aggregate in pavement mixtures. A total of ten different concrete mixtures containing recycled concrete aggregate (RCA) were designed to meet the requirements of Indiana Department of Transportation (INDOT) specifications. These included three different RCA replacement levels (30%, 50% and 100% by weight of the natural coarse aggregate) and two different cementitious systems (plain system – Type I portland cement only and fly ash system – 80% of Type I portland cement and 20% of ASTM C 618 Class C fly ash). The scope of the project included the evaluation and comparison of several properties of RCA and natural aggregates, evaluation and analysis of the effects of RCA on concrete properties, and modification of aggregate gradations and mixture composition in an attempt to improve the properties of RCA concrete. All ten mixtures were first produced in the laboratory (trial batches) and were subsequently reproduced in the commercial ready-mixed concrete plant. Each mixture produced in the ready-mixed plant was used to prepare several types of specimens for laboratory testing. The tests performed on fresh concrete included determination of slump and entrained air content. The mechanical properties of the hardened concrete were assessed by conducting compressive strength, flexural strength, modulus of elasticity and Poisson’s ratio tests. Concrete durability was assessed using a wide array of measurements, including: rapid chloride permeability (RCP), rapid chloride migration (RCM), electrical impedance spectroscopy (EIS), surface resistivity, free shrinkage, water absorption test, freeze-thaw resistance and scaling resistance. The test results indicated that the properties of plain (no fly ash) concrete mixtures with 30% RCA as coarse aggregate were very comparable to (in some cases even better than) those of the control concrete (0% RCA). Although mixtures with 50% RCA showed a reduction in durability and mechanical properties of up to 36%, the test results still met INDOT’s specifications requirements. The mechanical properties of plain concretes made with 100% RCA were measurably lower (16%-25%) than those of the control concrete. It should be pointed out, however, that these properties were still above the minimums required by INDOT’s specifications except for one mixture in which the w/c was increased to 0.47 to achieve workability. The use of fly ash improved the strength and durability of RCA concrete, especially at later ages. In particular, the properties of concrete with 50% RCA coarse aggregate were similar to the properties of control concrete. Similarly, the mechanical and durability properties of the mixture with 100% RCA coarse aggregate and 20% fly ash were better than those of a similar mixture prepared without fly ash. Even though, when compared to the fly ash concrete with 100% virgin aggregate the mechanical and durability properties of the 100% RCA concrete were up to 19% and 35% lower, it still met minimum requirements imposed by INDOT’s specifications.

Durability of Pavement Concretes Made with Recycled Concrete Aggregates

There is a growing trend to replace the traditional ingredients of concrete pavement mixtures with more sustainable materials from a perspective of both the cost of raw materials and the carbon dioxide footprint. The availability of quality natural aggregates, which make up about 70% to 80% of concrete (by volume), is becoming more limited because of environmental restrictions on quarrying operations and longer hauling distances. The other major concern is disposal of old concrete pavements, which unless used as fill or base material for construction of new roadways, will have to be placed in the landfills. In this study, recycled concrete aggregates (RCA) obtained from crushing old concrete pavement were used as coarse aggregates at 0%, 30%, 50%, and 100% replacement levels (by mass) for natural virgin aggregates (NVA). Concrete mixtures were designed and produced to meet the concrete pavement requirements for air content, slump, and flexural strength stipulated by the Indiana Department of Transportation. All concrete mixtures were produced with 18.5% to 20.0% of the cement replaced (by mass) with ASTM C618 Class C fly ash. The physical and mechanical testing involved evaluation of slump, air content, and development of both flexural and compressive strengths. In addition, durability was assessed with the freeze–thaw test, scaling test, rapid chloride permeability (RCP) test, and non–steady state migration test. The most advantageous dosages for replacing NVA with RCA for concrete pavements were found to be 50%, on the basis of fresh concrete properties and the results of strength and durability tests. The applicability of electrical impedance spectroscopy for quick performance appraisal is presented on the basis of the experimental relationship between the RCP charge and bulk resistance of concrete.

Quick Determination of Freeze–Thaw Durability of Concrete Aggregates Using the Indiana Department of Transportation Hydraulic Fracture Test Equipment

The freeze–thaw durability of carbonate aggregates can vary greatly, from durable to highly susceptible to freeze–thaw distress. Using nondurable aggregate in concrete pavement exposed to freeze–thaw cycles may lead to serious distress and greatly decrease the pavements service life. The testing needed to identify freeze–thaw durable aggregates can take several months to complete. The main objective of this study was to develop a reliable, quick test method for determining the freeze–thaw resistance of carbonate aggregates quarried in Indiana by using the hydraulic fracture test (HFT) equipment. Aggregate samples collected from 18 quarried carbonate sources that represented a range of freeze–thaw performance were subjected to HFT with the modified Indiana Department of Transportation (Indiana DOT) HFT equipment. Aggregates from the same sources were also used to produce concrete beams that were subjected to the Indiana DOT-modified AASHTO T161-B freeze–thaw test. This test evaluated the dilation of beams exposed to freeze–thaw cycles. The experimental data were analyzed statistically, and a linear regression model was developed to predict the average percent dilation of freeze–thaw test beams using parameters obtained from HFT results. Comparing the predicted dilations to the measured dilations gave an adjusted R2 value of .85 and indicated that the model has a high degree of certainty. The modified Indiana DOT HFT equipment, refined test procedures, and data analysis developed during this study are recommended as screening tools for predicting AASHTO T161–ASTM C666 test results in 8 days. However, further testing is necessary to refine and validate the model before it is fully implemented as an accepted standard.

Hydraulic Fracture Test to Determine Aggregate Freeze-Thaw Durability

The freeze-thaw durability of carbonate aggregates can vary greatly from durable to highly susceptible to freeze-thaw distress. Using nondurable aggregate in concrete pavement exposed to freeze-thaw cycles my lead to serious distress and greatly decrease the pavements service life. The testing needed to identify freeze-thaw durable aggregates can take several months to complete. The main objective of this study was to develop a reliable, quick test method for determining the freeze-thaw resistance of carbonate quarried aggregates in Indiana using the Hydraulic Fracture Test (HFT) equipment. Aggregate samples collected from 18 quarried carbonate sources from across Indiana that represented a range of freeze-thaw performance were subjected to HFT using the existing Minnesota Department of Transportation (MnDOT) HFT equipment and the newly developed Indiana Department of Transportation (INDOT) HFT equipment. Aggregates from the same sources also were use to produce concrete beams that were subjected to the INDOT modified American Association of State Highway and Transportation Officials (AASHTO) T161-B freeze-thaw test (ITM 210) which evaluates the dilation of concrete beams exposed to freeze-thaw cycles. The experimental data were analyzed statistically and linear regression models were developed to predict the average percent dilation and the durability factor of freeze-thaw test beams using parameters obtained from HFT results. Comparing the modeled and measured test results, the favored model predicts dilations based on the INDOT HFT results. These modeled dilations, when compared to measured dilations gave an adjusted R² value of 0.85, indicating the model has a high degree of certainty. The modified INDOT HFT equipment, refined test procedures and data analysis developed during this study are recommended as screening tools for predicting AASHTO T161/ASTM C666 FT test results in 8‐days. Further testing is recommended to refine and validate the models before they are fully implemented as an acceptance standard.

Joint Deterioration in Concrete Pavements

Concrete pavements located in cold climates have been experiencing premature joint deterioration. Entrapment of moisture in the joints saturates the surrounding concrete, rendering it susceptible to freeze–thaw damage. To identify and to isolate the variables that might be causing this localized deterioration, concrete cores were obtained from deteriorated and non-deteriorated sections of US 35, SR 38, and SR 3, located near Indianapolis, IN, and I-94, located near Michigan City, IN, USA. The visual evaluation of the condition of the pavement revealed that the drainage of the joints contributes significantly to their performance. Specifically, all deteriorated joint core holes drained poorly when compared with well-performing joint core holes or mid-panel joint core holes. Hardened air void parameters were determined following the procedure described in ASTM C457 and results for cores from deteriorated and non-deteriorated regions of the pavements were compared. The chemical and microstructural changes occurring in concrete were investigated using scanning electron microscope. Concrete panels with poor values of spacing factor and specific surface area were more prone to premature joint deterioration. Visual observation of coring sites on I-94 showed that unsealed joints performed better than sealed joints.

Investigation of Premature Distress Around Joints in PCC Pavements: Parts I & II

Some of the Indiana concrete pavements that have been constructed within the last 10 years have shown signs of premature deterioration, especially in the areas adjacent to the longitudinal joints. This deterioration typically manifests itself as cracking and spalling of concrete combined with the loss of joint sealant. These processes create a cavity in the joint area that traps water and, as a consequence, accelerates further deterioration of concrete during the freezing and thawing cycles. The objective of this study was to examine in details the microstructural and chemical changes in concrete extracted form the affected areas in an attempt to determine the cause of this premature deterioration. The investigation started with a detailed inventory of selected areas of affected pavements in order to identify and classify the existing types of distresses and select locations for collection of the cores. The cores have been collected from the following four locations: NB lines of I-65 near downtown Indianapolis, SR 933 near South Bend, Intersection of 86th Street and Payne Road in Indianapolis and a ramp from US67 to I-465E, also in Indianapolis. A total of thirty six 6-in. diameter cores were removed from pavements at these locations and transported to the laboratory where they were subjected to eight different tests: air-void system determination, Scanning Electronic Microscopy (SEM) analysis, X-ray diffraction (XRD) analysis, sorptivity test, freeze-thaw & resonance frequency test, resistance to chloride ion penetration (RCP) test and chloride profile (concentration) determination. The test results identified several cases of in-filling of the air voids (especially smaller air bubbles) with secondary deposits. These deposits were most likely the result of the repetitive saturation of air voids with water and substantially reduced the effectiveness of the air voids system with respect to providing an adequate level of freeze-thaw protection. In addition, the affected concrete often developed an extensive network of microcracks, showed higher rates of absorption and reduced ability to resist chloride ions penetration.

Concrete Capillary Porosity as It Relates to Durability of Pavements Built with Alkali-Silica-Reactive Aggregates

Several concrete pavements have been constructed in southwestern Minnesota using aggregates that recently have tested as being potentially deleteriously alkali-silica reactive. Standard ASTM test procedures were used. Most of these pavements fail to meet their design life. However, the rate of deterioration varies. Six pavement sites varying in age and performance were selected for comparison. Alkali-silica gel is present in all six pavements, even in the 36-year-old pavement still in good condition. Similar aggregate types were used for all six pavements. The coarse aggregate was a low-grade metamorphic quartzite, and the fine aggregate was a glacial sand obtained from various local sources. The relative capillary porosity of the concrete paste was examined using fluorescent dye epoxy impregnated with thin-section samples from each pavement site. Preliminary results suggest that the capillary porosity is linked to the durability of the concrete pavement. The best-performing concretes had a homogeneous capillary porosity that was moderate to low, and the poorer-performing concretes had paste with a capillary porosity that varied from high to low.