Jitendra Jain

Conventional Portland Cement and Carbonated Calcium Silicate–Based Cement Systems: Performance During Freezing and Thawing in Presence of Calcium Chloride Deicing Salts

The behavior of two cementitious materials during thermal changes associated with freezing and thawing in presence of calcium chloride deicing salts was examined. The two systems consisted of a conventional portland cement-based material and an alternative economically friendly cement that formed a solid by carbonating a calcium silicate–based cement. Low-temperature differential scanning calorimetry was used to quantify the phase changes associated with ice formation, eutectic solution transformation, and calcium oxychloride formation. Longitudinal guarded comparative calorimetry was used to detect the damage that developed as a result of the expansive pressures created by these phases when they form. In both systems exposed to low salt concentration, the damage was primarily caused by hydraulic and osmotic pressure. This type of damage was moderate at low degrees of saturation (e.g., <90%); however, as the degree of saturation increased, so did the damage. In conventional cementitious systems at higher salt concentrations, the damage that developed was mainly caused by the formation of calcium oxychlorides. However, in the cementitious materials made by carbonating calcium silicate–based cement calcium, hydroxide was not present. Therefore, at higher salt concentrations, calcium oxychloride did not form, and as a result, no damage developed.

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.

Effects of Deicing Salt Solutions on Physical Properties of Pavement Concretes

Salt solutions are used on pavement surfaces during wintry weather events to ensure safe driving conditions. In addition to sodium chloride (NaCl), which continues to be traditionally used as a deicer, solutions of calcium chloride (CaCl2) and magnesium chloride (MgCl2) are being increasingly used to provide a more consistent ice and snow control and thus ensure safe driving. This paper assesses the effects of three salt solutions (NaCl, CaCl2, and MgCl2) on several physical and mechanical properties of pavement concretes. These deicing solutions were used under simulated wetting–drying (W-D) and freezing–thawing (F-T) exposure regimes with total ion concentration of the deicers of 10.5 molal for W-D exposure and 5.5 molal for F-T exposure. Two types of concretes were used in the study: ordinary portland cement concrete and fly ash concrete, in which 20% (by mass) of cement was replaced by Class C fly ash. The physical changes of cylindrical specimens subjected to the W-D regime were monitored by ultrasonic pulse velocity measurements after every 2 weeks of exposure until the end of the test. At the end of the W-D exposure period, the same test cylinders were used to obtain the compressive strength of the concrete. The results of all measurements, combined with visual observations of the overall condition of the specimen, were used to assess the relative effect of deicers (and the exposure conditions) on both types of concretes. The overall findings from this research indicated that exposure to the CaCl2 deicer resulted, in general, in more severe changes in the physical and mechanical properties of both types of concrete used in this study.

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.

Physico-chemical changes in nano-silica and silica fume modified cement pastes in response to leaching

Leaching of calcium ions from cement pastes modified with silica fume and nano-silica, and the physico-chemical changes that this induces in the system are the focus of this paper. The pastes were subjected to slow (in deionised water) and accelerated (in 6M ammonium nitrate) leaching. Mass loss, increase in porosity and thermal analysis were used to quantify the physical and chemical changes in the system due to leaching. The modified cement pastes are found to exhibit better leaching resistance under both exposure conditions. It is shown that leaching in deionised water and cementing materials reaction are essentially coupled. When leached in ammonium nitrate, it is observed that the entire CH is leached from all the pastes, and pastes with very low initial CH contents suffer increased decalcification from C-S-H gel. It is shown that, when subjected to very aggressive leaching agents, a certain amount of CH acts as a buffer delaying C-S-H dissolution. The beneficial effect of nano-silica in controlling calcium ion leaching especially when subjected to accelerated leaching is brought out.

Investigation of Anti‐Icing Chemicals and Their Interactions with Pavement Concretes

The interactions of concrete specimens (both plain and with fly ash addition) with six different deicers was investigated by exposing them to solutions of sodium chloride (NaCl), magnesium chloride (MgCl2), calcium chloride (CaCl2), and the combinations of: sodium chloride with magnesium chloride (NaCl + MgCl2), sodium chloride with calcium chloride (NaCl + CaCl2), sodium chloride with agricultural by product – Ice Ban® (NaCl + Ice Ban®). In addition, control group of specimens was exposed to the deionized water. The exposures consisted of wet/dry (W/D) and freeze/thaw (F/T) cycles as well as a continuous storage in lime water at 23°C. The effects of various exposure conditions were evaluated based on the changes in the following: relative dynamic modulus of elasticity (RDME), ultrasonic pulse velocity (UPV), mass of specimens, length of specimens, mass of scaled material and compressive strength. In addition, absorption and chloride penetration measurements were performed for specimens exposed to various deicers at room temperature of 23°C. Finally, the qualitative visual evaluation of the appearance of the samples was also performed along with documentation of microstructural changes using the scanning electron microscopy (SEM). Among the deicer/anti‐icers tested, calcium chloride and magnesium chloride solutions caused comparatively higher degree of deterioration than other solutions. Although the ultimate extent of visual degradation of the specimens exposed to both of these deicers was very comparable, the onset of the degradation process in specimens exposed to magnesium chloride was significantly delayed when compared to the onset of deterioration of specimens exposed to calcium chloride. The best performance (least amount of damage) was observed for specimens exposed to sodium chloride solutions followed by the specimens exposed to the combination of sodium chloride with magnesium chloride and sodium chloride with calcium chloride. The test results indicate that F/T exposure conditions are much more severe than W/D regimes, even though the concentrations of deicers/anti‐icers used for F/T cycles were about 50% lower than those used for W/D cycles. Moreover, the addition of fly ash has a positive influence on performance of the concrete regardless of the type of the exposure regime.