Browsing by Author "Weiss, Jason"

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    Absorption and desorption properties of fine lightweight aggregate for application to internally cured concrete mixtures
    (ELSEVIER SCI LTD, 2011) Castro, Javier; Keiser, Lucas; Golias, Michael; Weiss, Jason
    Recently, substantial interest has developed in using fine lightweight aggregate for internal curing in concrete. Mixture proportion development for these mixtures requires the specific gravity, water absorption, and water desorption characteristics of the aggregate. This paper presents results from a recent study in which the properties of commercially available expanded shale, clay and slate lightweight aggregates (LWA's) were measured. This research measured the time-dependent water absorption response for the lightweight aggregate. The results indicate that a wide range of 24 h water absorption values exist for commonly used fine lightweight aggregates (e.g., absorption between 6% and 31%). Desorption was measured and it was found that between 85% and 98% of the 24 h absorbed water is released at humidities greater than 93%. These properties can be normalized so that they can be efficiently used in proportioning concrete for internal curing. Normalized plots of absorption and desorption demonstrate benefits for a single function that describes a large class of expanded shale, clay, and slate aggregate for use in internal curing. (C) 2011 Elsevier Ltd. All rights reserved.
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    Application of internal curing for mixtures containing high volumes of fly ash
    (ELSEVIER SCI LTD, 2012) De la Varga, Igor; Castro, Javier; Bentz, Dale; Weiss, Jason
    This paper focuses on testing performed on mixtures that would be consistent with the mortar portion of a concrete bridge deck mixture for many state departments of transportation. In this work a relatively large percentage of cement (40%, 60%, or 80% by volume) is replaced with Class C fly ash. To overcome concerns associated with slow set and early-age strength development that are often expressed with the high volume fly ash mixtures (HVFA), the water-to-cementitious materials ratio (w/cm) by mass has been reduced from a conventional value of 0.42 to 0.30. To overcome potential complications that the low w/cm may cause in terms of self-desiccation, internal curing (IC) with prewetted lightweight aggregate was used to reduce shrinkage and increase hydration. By adopting this approach (lowering the w/c and using IC) IC HVFA mixtures show additional benefits that should permit their broader application. (c) 2012 Elsevier Ltd. All rights reserved.
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    Characterizing Lightweight Aggregate Desorption at High Relative Humidities Using a Pressure Plate Apparatus
    (ASCE-AMER SOC CIVIL ENGINEERS, 2012) Pour Ghaz, Mohammad; Castro, Javier; Kladivko, Eileen J.; Weiss, Jason
    This paper describes the results of an experimental study that was performed to obtain desorption isotherms for a wide range of fine lightweight aggregates that are used commercially in North America. The desorption isotherms were determined for the entire gradation of the fine lightweight aggregates (as received). To obtain the desorption isotherms a pressure plate apparatus (porous plate) was used. The pressure plate enables the desorption isotherm to be measured at high relative humidities (beginning at 100%). In addition to providing experimental results obtained with the pressure plate method, desorption results obtained by gravimetric desorption and dynamic vapor desorption methods are also provided. The gravimetric desorption and dynamic vapor desorption methods are generally used at lower relative humidities (98% and 0% relative humidity). The results indicate that water leaves the fine lightweight aggregates at relative humidities as high as 99.9%. This suggests that internal curing water is available to the cement matrix even at relatively high water-to-cement ratio mixtures when the suction forces exerted by cement paste are small. The results of this work are helpful for the development of mixture proportioning techniques and numerical simulation for internally cured concrete mixtures. DOI: 10.1061/(ASCE)MT.1943-5533.0000422. (C) 2012 American Society of Civil Engineers.
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    Effect of sample conditioning on the water absorption of concrete
    (ELSEVIER SCI LTD, 2011) Castro, Javier; Bentz, Dale; Weiss, Jason
    ASTM C1585 is commonly used to determine the absorption and rate of absorption of water in unsaturated hydraulic cement concretes. Unfortunately, a wide range of relative humidities can exist in the samples after this relatively short conditioning period and such variation may considerably influence the test results. Three main variables were studied in this program: the water to cement ratio, the paste volume fraction, and the effect of sample conditioning. The results confirm that water absorption testing is considerably influenced by sample preparation. Samples conditioned at 50% relative humidity can show up to six times greater total absorption than similar samples conditioned at 80% relative humidity. Samples that were conditioned in the oven at 105 degrees C do not appear to follow a similar trend when compared with specimens conditioned in chambers at lower temperatures for a longer duration. The absorption is also influenced by the volume of paste in the samples. The experiments show that a lack of control on moisture content or lack of consideration of the material composition may lead to a misunderstanding of the actual absorption behavior. (C) 2011 Elsevier Ltd. All rights reserved.
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    The influence of the initial moisture content of lightweight aggregate on internal curing
    (ELSEVIER SCI LTD, 2012) Golias, Michael; Castro, Javier; Weiss, Jason
    This paper explores the potential for manufacturing internally cured concretes with lightweight aggregate (LWA) that has different initial moisture contents prior to mixing: oven-dry, 24 h pre-wetted, and vacuum saturated. Results show that when LWA is used in an oven-dry condition it can absorb water from the paste prior to set which will be returned to the system as internal curing water. When mixture proportion adjustments are properly made to account for the water absorbed by the aggregate before setting, the mixture can provide internal curing benefits. These beneficial aspects include increased hydration which leads to higher compressive strength, reduced water absorption, and reduced electrical conductivity (permeability). Further, these benefits include reduced autogenous shrinkage and a lower propensity for early-age cracking. (C) 2012 Elsevier Ltd. All rights reserved.
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    Using Isothermal Calorimetry to Assess the Water Absorbed by Fine LWA during Mixing
    (ASCE-AMER SOC CIVIL ENGINEERS, 2012) Castro, Javier; De la Varga, Igor; Weiss, Jason
    Fine lightweight aggregate (LWA) is being increasingly used for the manufacture of internally cured concrete. Internally cured concrete can be viewed as a concrete that contains fluid (water) in the pores of the LWA (or other porous inclusions) that can be released to the paste after setting. Most research performed on internally cured concrete assumes the LWA has been prewetted for some time before mixing (generally lab studies use 24-h soaking, whereas this value varies in practice). The research described in this paper investigated the potential for using aggregate that begins the mixing process from a different moisture state (i.e., not 24-h prewetting). Specifically, this paper considers oven-dry aggregate as a worst-case scenario to determine how much water would be absorbed by the LWA during the mixing and placement processes. To determine the amount of water absorbed by the LWA, isothermal calorimetry was used. Two different mixing scenarios were investigated, showing that 56-71% of the 24-h water absorption could be achieved using the worst-case scenario of oven-dry aggregates. Although the use of oven-dry aggregate would be extremely rare for a field application (except for possible application to bagged products), this approach could be extended to include fine LWA with other initial moisture conditions. DOI: 10.1061/(ASCE)MT.1943-5533.0000496. (C) 2012 American Society of Civil Engineers.
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    Water Absorption and Critical Degree of Saturation Relating to Freeze-Thaw Damage in Concrete Pavement Joints
    (ASCE-AMER SOC CIVIL ENGINEERS, 2012) Li, Wenting; Pour Ghaz, Mohammad; Castro, Javier; Weiss, Jason
    Fluid ingress is a primary factor that influences freeze-thaw damage in concrete. This paper discusses the influence of fluid ingress on freeze-thaw damage development. Specifically, this paper examines the influence of entrained air content on the rate of water absorption, the degree of saturation, and the relationship between the saturation level and freeze-thaw damage. The results indicate that whereas air content delays the time it takes for concrete to reach a critical degree of saturation it will not prevent the freeze-thaw damage from occurring. The results of the experiments show that when the degree of saturation exceeds 86-88%, freeze-thaw damage is inevitable with or without entrained air even with very few freeze-thaw cycles. DOI: 10.1061/(ASCE)MT.1943-5533.0000383. (C) 2012 American Society of Civil Engineers.
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    Water Absorption and Electrical Conductivity for Internally Cured Mortars with a W/C between 0.30 and 0.45
    (ASCE-AMER SOC CIVIL ENGINEERS, 2012) Castro, Javier; Spragg, Robert; Weiss, Jason
    Internal curing has emerged over the last decade as an approach to counteract the negative effects associated with self-desiccation in low water-to-cement ratio (w/c) mixtures. Specifically, much of the early research on internal curing focused on the reduction of autogenous shrinkage. Recent work has demonstrated, however, that internal curing can also be beneficial in reducing drying-shrinkage cracking, reducing the propensity for thermal cracking, reducing fluid absorption, and reducing ion diffusion in concrete. However, several aspects of internal curing still require closer examination. One of these aspects is the application of internal curing for mixtures with a wider range of water-to-cement ratios. This paper describes results from experiments that investigated the potential use of internal curing in mortar systems with w/c ratios of 0.30, 0.36, 0.42, and 0.45 that were cured under sealed conditions, in terms of water absorption and electrical conductivity. Test results show that internal curing reduces the water absorption in all the systems. Similarly, results obtained on electrical conductivity at late ages (1 year) also show a benefit. Care needs to be taken to analyze electrical conductivity results at early ages because of the increased amount of fluid resulting from the inclusion of the prewetted lightweight aggregate. DOI: 10.1061/(ASCE)MT.1943-5533.0000377. (C) 2012 American Society of Civil Engineers.