A New Mixture Proportioning Method for Performance- Based Concrete

Glosser D., Suraneni P., Isgor O.B., Weiss W.J.

This paper proposes an approach to estimate reaction kinetics for major fly ash glassy oxides in cementitious mixtures. The approach is compared to experimental results from multiple independent datasets. The kinetic model is based on the rate limiting step for various oxides and phases using the general form of a widely used model for ordinary portland cement (OPC)-based systems. The empirical parameters in the model were fit from dissolution studies for glass oxides in two fly ashes from literature using a nonlinear optimization algorithm. The outputs of the model provide the inputs needed to introduce reaction kinetics into thermodynamic simulations at non-equilibrium conditions. The model is used to determine the amount of each phase that can react by estimating the dissolved mass of each major cement phase and fly ash glass oxide at different ages. This approach enables accurate modeling predictions of solid hydration products (such as calcium hydroxide and ettringite), pore solution pH, and pore solution chemistry at any age for any OPC/fly ash system. Results from the model and thermodynamic calculations are compared to a modeling approach without kinetic constraints on the fly ash, assuming 100% reactivity. The prediction of reaction products made assuming 100% fly ash reactivity significantly differs from experimental values when a fly ash kinetic model is not used. Predictions are greatly improved when the model is used. The model can be used as a framework for future modeling efforts, and the empirical parameters be updated as additional dissolution studies and thermodynamic data become available.

Suraneni P., Hajibabaee A., Ramanathan S., Wang Y., Weiss J.

Tests to determine the reactivity of supplementary cementitious materials (SCMs) by using isothermal calorimetry and thermogravimetric analysis have been proposed. In one such test, the heat release and calcium hydroxide consumption of SCMs mixed with calcium hydroxide (3:1 ratio of calcium hydroxide and SCM) at 50 °C in a 0.5 M potassium hydroxide environment are measured. In this study, we show the results of such testing for a large variety of SCMs and fillers, ranging from conventional materials such as fly ash, slag, silica fume, quartz, and limestone, to alternative materials such as calcined clays, municipal solid waste incineration fly ash, basic oxygen furnace slag, ground lightweight aggregates, ground pumice, ground glass pozzolan, and basalt fines. A total of 54 SCMs are tested using this approach. Results show that even among SCMs of the same type, there is considerable difference in the heat release and calcium hydroxide consumption, likely due to differences in amorphous content, chemical composition, and fineness, leading to different reactivities. Based on the response in the test, SCMs are classified into inert, pozzolanic, and latent hydraulic; the pozzolanic and latent hydraulic materials are further classified into less reactive and more reactive. The relationship between heat release and calcium hydroxide consumption depends on the chemical composition of the SCMs, and SCMs with high calcium, high alumina, and high silica contents show different relationships (determined by the slope of the heat release vs. calcium hydroxide plot).

Bharadwaj K., Glosser D., Moradllo M.K., Isgor O.B., Weiss W.J.

Many properties of concrete are related to its pore volume and pore structure. This paper describes an approach to predict gel and capillary pore volumes and other hardened properties of pastes using the pore partitioning model, and scaling these calculated properties to concrete by including entrained and entrapped air and aggregates. This paper focuses on illustrating how parameters that can be used for determining the freeze-thaw performance can be computed using a critical saturation model. Specifically, the degree of saturation and formation factor of the concrete are predicted when the matrix pores are saturated. Based on the model simulations, the secondary rate of sorption can be estimated using the formation factor to predict the potential for reaching a critical degree of saturation which is a measure of concrete's resistance to freeze-thaw damage. This approach allows for the evaluation of the performance of concrete mixtures with a wide variety of binder compositions and mixture proportions. The model predicts the saturated formation factor with a maximum error of 13% and the matrix saturation with a maximum error of 7%. The model can also be used to provide insight into the amount of entrained air needed for a given replacement and reactivity of binder.

Glosser D., Choudhary A., Isgor O.B., Weiss W.J.

Tsui-Chang M., Suraneni P., Montanari L., Muñoz J.F., Weiss W.J.

Trejo D., Hendrix G.

Weiss W.J., Spragg R.P., Isgor O.B., Ley M.T., Van Dam T.

This paper relates a fundamental material property (the formation factor) with the use of electrical resistivity for acceptance tests of concrete. The paper begins by defining the formation factor. It then relates the formation factor to the rapid chloride permeability test. The formation factor is then related to a predictive model that can be used to determine a corrosion limit state by describing the transport of chloride ions and determining the time required for the onset of depassivation corrosion initiation in a reinforced concrete element. The paper discusses factors that influence electrical resistivity testing along with methods to determine the pore solution conductivity which have been adopted in an AASHTO provisional specification. While the specification will undoubtedly be refined over time and models will require further calibration based on rigorous evaluation and improvement in the coming years, this framework has great potential to directly relate measured concrete properties to the long-term durability performance of concrete structures.

Suraneni P., Monical J., Unal E., Farnam Y., Weiss J.

Whatley S.N., Suraneni P., Azad V.J., Isgor O.B., Weiss J.

AbstractCertain chloride-based deicing salts can react with calcium hydroxide in cement paste to form calcium oxychloride. Calcium oxychloride formation results in expansive pressures that damage c...

Suraneni P., Azad V.J., Isgor O.B., Weiss W.J.

Premature damage has been observed at the joints in numerous concrete pavements where calcium chloride and magnesium chloride deicing salts have been used. This damage results from a reaction between the deicing salt and the calcium hydroxide (CH) in the hydrated cement paste. This reaction leads to the formation of an expansive product known as calcium oxychloride (CAOXY). The use of supplementary cementitious materials as a replacement for cement has been proposed to reduce the CH that is available in the mixture to react with the deicing salts. Reducing the CH can reduce the amount of CAOXY that forms. In this study, mixtures representative of paving concrete were made with cements and fly ashes from across the country. CH amounts were determined by using thermogravimetric analysis, and CAOXY amounts were determined by using low-temperature differential scanning calorimetry. Various replacement levels of fly ash were used to demonstrate that the main parameter that influences the amounts of CH and CAOXY that form is the replacement level of fly ash. This paper proposes that a prescriptive specification requiring 35% cement replacement by volume with fly ash would reduce the damage caused by CAOXY formation and further proposes a performance specification to limit the CAOXY formation to below 15 g/100 g paste.

Weiss W.J., Barrett T.J., Qiao C., Todak H.

This paper proposes that the formation factor can be used in performance-based specifications as a fundamental measure of the transport properties of concrete. The formation factor can be measured using a concrete cylinder that is sealed until the age of testing and in either the sealed or fully saturated condition at the time of testing. The proposed method is rapid, easy to perform, fundamentally related to service life models, and is applicable to a wide range of binder compositions. The formation factor is defined herein as the ratio of the electrical resistivity of the bulk sample and the resistivity of the pore solution. The role of temperature, pore solution dilution, and moisture conditioning on the measured results is discussed. The paper then provides a relationship between the formation factor and service life for bridge decks and illustrates how this approach could be used for both a specification and for quality control/quality acceptance. It is recommended that the testing method be standardized, though the performance limits of the formation factor may be dependent on the type and geometry of the structure, the location of the structure, the exposure conditions, and the risk associated with damage to the structure.

Suraneni P., Azad V.J., Isgor B.O., Weiss W.J.

Over the last decade many concrete pavements in North America have begun to show excessive damage at the joints. This damage appears to be due to two primary causes: classic freeze-thaw damage due to local saturation caused by the pooling of water at the joints, and formation of an expansive phase known as calcium oxychloride due to a reaction between chloride-based deicing salts and calcium hydroxide in concrete. This letter explores the formation of calcium oxychloride in cementitious matrices based on constituent materials and mixture compositions. Low temperature differential scanning calorimetry and thermogravimetric analysis were used to quantify the amount of calcium oxychloride and calcium hydroxide, respectively. Thermodynamic modeling was used to predict calcium hydroxide contents from the constituent material compositions. It is shown that calcium oxychloride contents are well correlated with calcium hydroxide contents in cementitious pastes. Supplementary cementitious materials, such as fly ash and slag, can reduce calcium oxychloride formation by reducing the amount of calcium hydroxide. Complexities in the determination of reactivity of supplementary cementitious materials based on their replacement level and different water-to-cement ratios are discussed. Although it is clear that supplementary cementitious materials are beneficial in reducing calcium oxychloride formation, additional analysis tools are needed to more accurately quantify the specific mechanisms (such as dilution, pozzolanic or hydraulic reaction, changes in cement hydration) that result in the beneficial aspects of each supplementary cementitious material.

Monical J., Unal E., Barrett T., Farnam Y., Weiss W.J.

Deterioration has been observed at the joints of many portland cement–based concrete pavements in midwestern U.S. states. It has been shown that this damage can be caused by either classic freeze–thaw behavior triggered by high saturation levels or a chemical reaction that occurs between the deicing salt (in this study, calcium chloride) and the cementitious matrix. The objective of this study was to show that low-temperature differential scanning calorimetry could be used to quantify the potential for the chemical reaction between the salt and matrix (i.e., calcium oxychloride formation). The formation of calcium oxychloride is expansive and may lead to significant cracking and spalling without exposure to freeze–thaw cycles. This study examined pastes made with ordinary portland cement; portland limestone cement; and portland cement combined with fly ash, slag, or silica fume. The results indicate that the amount of calcium oxychloride formation that occurs is not significantly different between ordinary portland cements and portland limestone cements. The addition of supplementary cementitious materials reduces the formation of the calcium oxychloride, presumably because of the reduction of calcium hydroxide from dilution, the pozzolanic reaction, and a reduction in the alkali content in the pore solution. The results also indicate that sealers can be used to create a barrier between the salt and the calcium hydroxide or that they can react with the calcium hydroxide, thereby reducing the amount of calcium oxychloride.

Farnam Y., Wiese A., Bentz D., Davis J., Weiss J.

Magnesium chloride (MgCl 2 ) is used in deicing applications due to its capability to depress freezing temperatures to a lower point than other salts such as sodium chloride (NaCl). The constituents of concrete (i.e., pores solution, calcium hydroxide, aluminate phases, and calcium silicate hydrate gel) can alter the MgCl 2 –H 2 O phase diagram when it is used to interpret the performance of concrete. Different chemical reactions may concurrently occur between MgCl 2 and cementitious constituents to form brucite, Friedel’s salts, magnesium silicate hydrate, magnesium oxychloride, and/or secondary calcium oxychloride. In this study, it was observed that MgCl 2 can be entirely consumed in concrete by the chemical reactions and produce CaCl 2 . As such, it was found that MgCl 2 interacts significantly with a cementitious material and it follows a response that is more similar to the Ca(OH) 2 –CaCl 2 –H 2 O phase diagram than that of the MgCl 2 –H 2 O phase diagram. Mortar samples exposed to low concentration MgCl 2 solutions ( 2 and cementitious constituents at room temperature (23 °C). These chemical reactions occurred rapidly (within 5–10 min) and caused a significant decrease in subsequent fluid ingress into exposed concrete.

Gardner L.J., Bernal S.A., Walling S.A., Corkhill C.L., Provis J.L., Hyatt N.C.

Magnesium potassium phosphate cements (MKPCs), blended with 50 wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on 25 Mg, 27 Al, 29 Si, 31 P and 39 K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthophosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium phosphate phase was formed, however, no significant Al–O–P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC.

Gao M., Heeren N., Wong H.S., Myers R.J.

Abstract Due to the vast landscape of low carbon concretes that have been or can be developed, traditional empirical methods are impractical for comprehensive assessment of concrete performance. Here, we describe Panoramix 1.0, a Python-based tool that can predict physical and chemical properties of hydrated cements, and durability and environmental impacts of concretes. Applying it to CEM I concrete as a case study, we investigate the cement composition effects on the freeze–thaw resistance indicator (time to critical saturation degree, t CR ). Results indicate that chemical composition of raw materials including Fe2O3 may influence freeze–thaw resistance, which is usually not considered in the current scheme of durability assessment. The results also show how the design space (i.e., feasible cement compositions) could be found for different types of concrete at specified minimum freeze–thaw resistance. We validate Panoramix by comparing its ranking of 28 concrete samples in terms of freeze–thaw performance (t CR ) with experimental data for relative dynamic modulus of elasticity (RDME) reported in ten publications and measured using procedures from four different standards. By combining the composition-freeze–thaw resistance modelling with a life cycle assessment model, we show that the climate change impact (100-year global warming potential) per m3 CEM I concrete can be reduced from 313 to 286 kg CO2-eq. by decreasing the clinker-to-cement ratio while reducing t CR from 7 to 5.5 years.

Bharadwaj K., Weiss W.J., Isgor O.B.

Glosser D., Russell L., Striby P.

Glass fiber and glass fiber-reinforced polymers are of interest to engineers for a wide variety of applications, owing to their low weight, high relative strength, and relative low cost. However, management of glass fiber waste products is not straightforward, particularly when it is part of a composite material that cannot be easily recycled. This is especially the case for physically large structures such as wind turbine blades. This chapter deals with the challenges of managing this growing waste stream and reviews the structure and chemistry of glass fiber and glass fiber-reinforced polymers used in wind turbine blades, the separations processes for extracting the glass fiber from the thermoset resin, and end-of-life options for the materials. Thermodynamic evidence is reported and evaluated for a novel end-of-life solution for wind turbine waste: using it as a supplementary cementitious material.

Choudhary A., Ghantous R.M., Bharadwaj K., Opdahl O.H., Isgor O.B., Weiss W.J.