Patent Application
20150007752
Provided herein are compositions comprising concrete and one or more phase change materials (PCMs), and their uses, for example, in preventing or reducing thermal damage in a cementitious system.
There is a need to develop thermal damage resistant and energy-efficient materials for building structures and infrastructure facilities.
In one aspect, provided herein is a composition comprising concrete and one or more PCMs for prevention or reduction of thermal damage in a cementitious system.
In another aspect, provided herein is a composition for controlling heat of hydration related thermal excursions in a cementitious system, the composition comprising concrete and one or more PCMs.
In one embodiment, the thermal damage comprises:
In one embodiment, the cementitious system is a hydrating or well-hydrated cementitious system.
In another embodiment, the concrete comprises stratified PCM layers. In another embodiment, the PCM in adjacent PCM layers are the same and/or different.
In another embodiment, the composition has a compressive strength of 500-25,000 psi. In another embodiment, the composition has a compressive strength of 1,000-20,000 psi. In some embodiments, a non-PCM material, non limiting examples of which include quartz, silica fume, fly-ash, blast furnace slags, natural pozzolans, and the likes, may be further included in the compositions provided herein to increase the compressive strength of compositions provided herein. In some embodiments, compositions provided here that further comprise silica fumes can improve the elastic modulus (E) of the composition.
In another embodiment, the composition further comprises one or more of fly-ash, slag, quartz, silica fume, a porous material such as both natural and manufactured lightweight aggregate inclusions of a porous nature, which are able to serve as reservoirs for the PCM, and either non-porous or slightly porous materials such as commonly used aggregates comprised of granite, limestone, etc.
In another embodiment, the PCM is a liquid that is included in a porous, inorganic, aggregate reservoir.
In another embodiment, the PCM is a solid that can undergo a phase transition to another state, such as a liquid. In another embodiment, the PCM is a liquid that can undergo a phase transition to another state, such as a solid.
In another embodiment, the PCM is of an organic nature. Non-limiting examples of organic PCMs include wax or paraffins, polyols, such as trimethylol ethane, and fatty acids, such as lauric acid. In another embodiment, the PCM is an inorganic PCM. Non-limiting examples of inorganic PCMs include salt hydrates and molten salts. Other examples of PCMs are described for example in Sharma et al., Renewable and Sustainable Energy Reviews 13 (2009) 318345.
In some embodiments, the PCM comprises a microcricapsulated structure, wherein the PCM is encapsulated within a shell. In some embodiments, the shells are generally stable or substantially stable to the mixing with cementitious material to the extent that the encapsulated PCMs retain their desired properties.
In some embodiments, the composition is a paste. In other embodiments, the composition is a mortar. In some embodiments, the composition is a concrete composition.
In another embodiment, the % of PCM in the compositions provided herein, by volume, is 0.5% to 50%, 1 to 30%, 2 to 20%, or 3 to 10%. In some embodiments, the volume and/or the dispersion of the PCM in the compositions provided herein are controlled in providing the benefits provided herein.
In other embodiments, the thermal damage is controlled for thermal excursions in sub-ambient and above-ambient temperatures. In another embodiment, the thermal damage is controlled for thermal excursions in the range of −15° C. to 70° C., measured in the composition. In another embodiment, the thermal damage is controlled for thermal excursions in the range of 15° C. or less. In another embodiment, the thermal damage is controlled for thermal excursions in the range of 15° C. or more, or of 20° C. to 50° C.
In another embodiment, the PCM shows a phase transition in the range of −15° C. to 65° C. In another embodiment, the PCM shows a phase transition in the range of 5° C. to 65° C. In another embodiment, the PCM has a phase transition temperature close to the freezing point of water, such as, for example, −15° C. to 10° C., −5° C. to 5° C., or −3° C. to 3° C.
In another embodiment, the PCM Shows a phase transition enthalpy of 20 joules/g to 500 joules/g. In another embodiment, the PCM shows a phase transition enthalpy of 80 joules/g to 300 joules/g.
In another aspect, provided herein is a cementitious structure comprising the composition provided herein, wherein the structure has a high surface to volume ratio and is selected from a floor, a parking lot, and a side walk pavements, slab on grade, bridge decks, and the likes, and from girders, mass concrete sections including columns, bridge piers, dam elements, and the likes.
In another aspect, provided herein is a cementitious structure comprising the composition provided herein, wherein the structure has a large concrete section and is selected from girder darns, and concrete sections including columns, bridge piers, and the likes.
As used herein a “phase change material” or PCM refers to a material that is capable of storing latent heat in the form of thermal energy corresponding to the phase transition temperature of that phase change material (PCM). Phase change can be in the following forms: solid-solid, solid-liquid solid-gas, liquid-gas and vice versa.
In one aspect, provided herein is a composition comprising concrete and one or more PCMs for prevention or reduction of thermal damage in a cementitious system, wherein the concrete comprises stratified PCM layers, and the thermal damage comprises:
In another aspect, provided herein is a composition comprising concrete and one or more PCMs for prevention or reduction of thermal damage in a cementitious system, wherein the PCM is a solid, or a liquid, included in a porous, inorganic, aggregate reservoir, and the thermal damage comprises:
Embodiments within the above mentioned aspects are disclosed herein, as will be apparent to the skilled artisan upon reading this disclosure.
In some embodiments, the PCM employed herein comprises or is Micronal® PCM available from BASF Corporation. Micronal® is a PCM, which completes a phase change from solid to liquid at 21° C., 23° C. or 26° C. and vice versa and in doing so can store or release heat Micronal® contains in the core of the microcapsule (size around 5 μm) a latent heat storage material made from a special wax mixture. When there is a rise in temperature above a defined temperature threshold (e.g., 21° C., 23 C or 26° C.), this absorbs the excessive heat energy and stores it in phase change. When the temperature falls below the temperature threshold, the capsule releases this stored heat energy again.
Cracks can develop in concrete elements when volume changes related to chemical reactions, and thermal or moisture fluctuations are prevented due to end, base, or internal (aggregate) restraint. Early-age thermal cracking can accelerate deterioration, increase maintenance costs, and reduce the service-life of structures.
The thermal cracking susceptibility of a restrained concrete element is dictated by a variety of factors including the: (1) mixture composition of concrete which impacts the heat evolved during the cement reactions, (2) ambient environmental conditions such as wind speed, temperature at placement, and diurnal day-night thermal fluctuations, and (3) geometry (size, shape, aspect ratio) of the concrete element, and the insulation effects of formwork which influences self-heating (and semi-adiabatic temperature increase) and the development of thermal gradients through the cross-section. While these factors can be interrelated, concerns related to the thermal cracking risk may be addressed if the peak (critical) temperature excursion achieved during the cement reactions and the cool down rate can be controlled.
A technology, such as that provided herein, which is capable of reducing the maximum section temperature without affecting the rate of early property development would act to: (1) minimize the temperature/strain gradient by maintaining a uniform temperature through the element's cross section, (2) reduce the magnitude of thermal deformations that may be expected as the section cools down (and contracts) from the time of cast through the diurnal temperature cycle by restricting the maximum temperature rise, and (3) minimize thermal/microstructural effects (temperature rise, gradients and deformations, increased porosity) related to an auto-catalytic acceleration of the cement reaction rate and an increase in section temperature) in a thermally-insulated environment as might occur in the interior of a bridge-pier, large footing or a column. The critical temperature rise, cool-down rate, and the temperature and stress development (gradient and magnitude) inside a structural element depends on the geometry, mechanical degree of restraint, and the concrete mixture proportions and characteristics.
By resisting a temperature change, i.e., by absorbing and releasing heat, PCMs can limit deformations associated with temperature rise, thus limiting critical strain gradients and reducing the risk of thermal cracking at early-ages. The incremental addition of a PCM can progressively suppress temperature rise in a hydrating cementitious system. In some situations, by limiting the peak temperature, the addition of PCMs can also result in an altered cool down rate by reducing the temperature differential between the concrete and the environment. It is also contemplated that cement-PCM composites can be tailored to shift the peak temperature to a later time (age) to allow the concrete to gain strength and better resist cracking.
In addition to the early-age benefits mentioned above, PCM-embedment in cementitious materials can provide performance benefits even at longer time-scales. For example: in most cases, the cement paste and aggregate fractions in concrete, and the concrete and structural support elements (girders, beams) have differing thermal deformation coefficients. This results in thermal deformation incompatibilities for a given thermal excursion (heating or cooling) between the paste and the aggregate or the concrete and its restraining/supporting element. When the condition is such that an aggregate inclusion, structural element, or the sub-grade restrains deformations (e.g., as provided by non-shrinking aggregate inclusions in cooling driven shrinkage), tensile stresses develop. When the residual (tensile) stress developed exceeds the strength of the material, cracks develop. A similar effect manifests when a concrete section expands or contracts due to diurnal or seasonal (e.g., freeze-thaw cycling) temperature variations against structural restraint. When thermal deformations and stresses develop repetitively over an extended period (in-service), cyclic loading of this nature induces fatigue-type thermal damage.
By reducing the number of imposed temperature cycles and the cyclic stress range (by limiting the magnitude/extent of temperature change), the addition of PCMs reduces the rate/extent of crack extension in the system. Retarding crack extension makes the material more damage tolerant. The ability to limit fatigue damage is a considerable benefit in extending the service-life of structures.
PCMs and entrained air can act as a two-part freezing protection system for concrete elements. Here, the use of PCMs with a phase transition temperature close to the freezing point of water is contemplated to reduce the number and intensity of freezing events in the system while entrained air would protect against expansive ice crystallization related damage. In addition to improved concrete durability, this approach also offers advantages such as skid resistance, thus adding to the safety of transportation infrastructure.
For concrete pavements, when a PCM-rich concrete layer is placed at the ride surface, it is contemplated to delay the drop in the overall section temperature. In some embodiments, in mild to moderate freezing zones where the temperature drops slightly below the freezing point of water, the heat of solidification of the PCM can be sufficient to consistently maintain PCM-containing concrete elements above the freezing point of the concrete's pore solution.
The potential benefit of PCMs in exposed concrete elements can be illustrated using the following example. In a wet pavement or bridge deck surface with 0.50 kg of freezable-water per square meter, 167 kJ/m2 of energy should be supplied to prevent the water from freezing (since the latent heat of fusion of water is 334 kJ/kg. If a PCM with an enthalpy of solidification of 100 kJ/kg is incorporated in the concrete section, 1.67 kg of well-dispersed PCM is included per square meter of the pavement or bridge deck surface to prevent freezing. The required quantity of the PCM can be incorporated as microencapsulated particles or incorporated directly into the porous aggregates akin to internal curing as accomplished using porous reservoirs. The efficiency of the PCM addition would further depend on the properties of the PCM (enthalpy of phase change, phase transition temperature, thermal conductivity), the mode of PCM incorporation and its efficiency of distribution in concrete, and the intensity of imposed freeze-thaw cycles. In some embodiments, doping the PCM with conductive particulate inclusions is contemplated to improve freeze-thaw damage.
In some embodiments, organic and non-polar PCMs are employed according to this disclosure. Cementitious mixtures are proportioned with a water-to-cement ratio (w/c) between 0.42 and 0.45 (0.42<w/c<0.45) to ensure that the early-age deformations are purely thermal in nature while neglecting autogenous effects. The characterization of material properties relevant to cementitious composites are performed at intervals of 1, 3, 7, and 28 days. First, the compressive strength of the cementitious systems are determined as per ASTM C39/C109 and the elastic modulus using ultrasonic (compressional-wave) methods. Second, determinations of the isothermal and semi-adiabatic thermal signature of the cementitious mixtures are carried out. This information is used to identify the rate and extent of the cement reaction and the relevant thermal excursion that may be expected in the system. Third, differential scanning calorimetry (DSC) is used to characterize the enthalpy of phase change of the pure PCM and the PCM-cement paste composite. The DSC scans are also used to determine the phase transition temperatures. If the temperature rise under semi-adiabatic conditions is noted to alter the rate of reaction considerably, the material property evaluations of the cementitious formulations is performed at other suitable (lower/higher) curing temperatures to accurately characterize the material properties.
In some embodiments, microencapsulated PCMs are used in cementitious formulations, Microencapsulated PCMs are available in several particle sizes/shapes that facilitate their direct addition into cement pastes or concretes. In some embodiments liquid-PCMs are incorporated into porous (inorganic) aggregate reservoirs. Such incorporation is performed by employing methods of vacuum saturation or miscibility linked fluid-displacement to impregnate porous media which can serve as thermal regulation devices in concrete. A detailed characterization of the pore volume-and-distribution (using porosimetrie and image analysis methods) of the PCM-host reservoir, and the density, viscosity and surface tension of the PCM is carried out to relate these parameters to the infiltration efficiency. The efficiency of the infiltration process and the suitability of the porous host (e.g., perlite, shale, or ceramic inclusions) is determined based on a maximum-filling criterion, as in general, a larger extent of filling would translate to better heat absorption and release behavior. The infiltration method and porous medium which achieve maximal pore-filling by the PCM are used for further testing. To avoid the movement of the PCM from the pores of the host to the matrix during melting, the porous inclusions in this study are coated with a layer of cement paste after PCM infiltration. As to PCM incorporation in porous lightweight aggregates, vacuum saturation is used at different times, vacuum saturation followed by ambient absorption, and long term ambient absorption. In lightweight aggregates with 25% porosity, 15% incorporation with a PCM is obtained. The porous inclusions, when coated with a layer of cement paste provide 3-day strengths comparable to those of specimens without PCM.
In some embodiments, the mechanical properties and thermal (isothermal and semi-adiabatic) signatures of cement-PCM composites are evaluated for a variety of PCM parameters. Electron microscopy is used to observe two dimensional microstructures of cement paste-PCM composites.
In some embodiments, the cementitious system used herein comprises portland cement. Portland cement can, in some embodiments, have an alkaline pH, for example, of >12.7, and contain for example a mixture of sodium and potassium hydroxides. Thus, in some embodiments, the performance of PCMs used in the compositions is determined in contact with deionized water and simulated concrete pore solutions of varying ionic strength when: (1) present in capsules, (2) present as a bulk liquid, and (3) infiltrated into a porous aggregate. In some embodiments, the thermal cycling stability of the PCM are evaluated using DSC measurements to cyclically measure the enthalpy of phase change during heating and cooling cycles. In some embodiments, the PCM-cementitious composites are tested to determine the bulk properties of the PCMs, such as, heat absorption and release, over multiple temperature change cycles.
In some other embodiments, the ability of PCMs to mitigate thermal stresses and cracking in restrained concrete elements is determined. Instrumented, invar dual-ring setups are used to quantify residual strain/stress development in cement pastes and mortars (with and without PCMs) under realistic (environmental and concrete) temperature conditions. The temperature profiles are generated by: (1) placing the restrained element in an enclosure provided with insulation and/or environmental regulation (temperature and humidity) to mimic semi-adiabatic or ambient environmental conditions, or (2) circulating temperature-conditioned fluids through a thermal conduction assembly maintained in contact with the restrained element. In some embodiments, customizable temperature profiles, peak-mixture temperatures and concrete cool-down rates are determined to test a variety of combinations as related to the mixture proportions, construction methods and environmental conditions.
In some embodiments, the residual stresses are quantified with a focus on: (a) determining the peak (compressive/tensile) stress developed and the rate and extent of (thermal) stress change (reduction) upon PCM addition, (b) the rate of post-setting stress development and the timing of compressive-to-tensile stress reversals, and (e) evaluating the risk (and-time) of thermal cracking based on an assessment of the crack resistance capacity of the material, in some embodiments, a comparison of the elastic and residual stresses are carried out to determine if changes in the thermal environment of the material impact the rate/extent of stress relaxation in materials. These evaluations arc carried out on paste and mortar formulations containing: (i) encapsulated PCM, (ii) PCM in porous inclusions, (iii) liquid PCMs, and (iv) PCM in multiple forms (combination of bulk-liquid, microencapsulated, in porous inclusions), in addition to conventional (non-PCM) mortar specimens.
In some embodiments, the extent of thermal stress reduction is quantified for varying volume additions of PCMs. In addition to early-age evaluations, thermal cycles corresponding to the extreme diurnal temperature variation in different geographical locations are imposed on instrumented mature (after 28 days of curing under sealed conditions) mortar slab/ring geometries under sealed/drying conditions for a minimum period of 90 days (180 beating/cooling cycles). By measuring the mortar temperature at the interior/surface, and quantifying stress (strain) cycling, the ability of PCMs to limit temperature fluctuations, thermal deformations and delay fatigue damage in restrained elements over longer-time scales, by providing multi-cycle phase change relief, is determined. Thus, in some embodiments, the ability of the compositions provided herein to mitigate early-and-later age thermal damage-and-cracking concerns in restrained concrete elements is determined.
In some embodiments, the ability of PCMs in reducing the freeze thaw damage propensity of exposed concrete elements is determined. In some embodiments a proper PCM (based on the transition temperature, heat of phase change) and its method of delivery to ensure a suitable dispersion of the PCM in the system are selected. In some embodiments, the PCM type/dosage developed from the DSC studies are integrated with dispersion quantifications to ensure that the PCM-assembly provides self-warming abilities to concrete. It is contemplated that by releasing phase-change linked heat, the PCM can help maintain the pore-solution in the liquid state for a longer duration. In some embodiments, such is beneficial during short, or limited magnitude freezing cycles as the addition of a PCM can act to reduce the number of freeze thaw cycles imposed on the concrete element.
In some embodiments, measurements of the internal and ambient temperature (in PCM incorporated and traditional cementinous systems) are combined with dynamic assessments of thermo-mechanical parameters (volume change with temperature, stiffness loss, heat flow) of specimens saturated to different moisture levels with and without air entraining agents. In some embodiments, the improvement in freeze-thaw behavior in materials exposed to a critical number of freeze-thaw cycles (for a constant moisture level) depending on the formulation. i.e., for conventional concrete, PCM-based concrete, or a concrete containing both PCMs and entrained air is determined. In some embodiments, “bridge-deck” sections for several geographic locations are simulated to be subjected to cyclic freeze-thaw events while mapping the temperature, strain, and the number of freeze-thaw cycles to macroscopic failure (based on reduction in dynamic elastic modulus) expected with and without the use of PCMs. In some embodiments, such results are used to provide calibrated tools which incorporate material models of heat transfer, environmental exposure information, deformation and damage mechanisms, and composite mixture proportioning strategies to predict freeze-thaw behavior and thus to specify PCM-based solutions for freeze-thaw resistant infrastructure.
In some embodiments, the compositions provided here are also useful for reducing the amount of energy required to heat and/or cool a building. Thus employed, the compositions provided herein can ensure heat storage (when the temperature increases as heat is supplied by incident solar radiation) and heat release (when the external environment cools), thereby decreasing the frequency of internal air temperature swings and keeping ambient internal temperatures closer to “optimal” for a longer duration of time.
In some embodiments, instrumented, thermally insulated custom concrete enclosures are built in the laboratory (approximately 1 ft3) to simulate as typical building exterior envelope. Several variations of roof slabs cart include: (1) conventional concrete (or mortar), (2) a conventional concrete sandwich panel containing typical thermal insulation material (such as polystyrene of fiberglass with a R value of 3-to-4 per inch of thickness), (3) a concrete containing encapsulated PCM at a selected dosage, (4) a concrete containing hulk liquid PCM, (5) a concrete where the PCM is contained in porous inclusions, and (6) a concrete containing PCMs in multiple forms, i.e., encapsulated, inclusion contained and bulk liquid. The simulated roof slab are heated cyclically using a light-source for between 10-to-12 hours to simulate daytime solar activity and then switched off to simulate night-time conditions. The simulated day-night cycles are repeated over an extended time-scale to determine the efficiency of each of these systems in thermal cycling related energy-conservation in terms limiting heat-transfer and maintaining fixed conditions inside the enclosure. The enclosures are provided with temperature sensing probes to monitor the internal, surface (wall and roof), and air temperatures. Further, the relative humidity variation in the internal environment will also be monitored.
In some embodiments, PCM cement compositions selected based in part on the methods described herein are used to construct field-scale instrumented roof-slabs for an enclosure (1 m3) along with a conventional concrete slab for comparison. The field-scale tests are conducted in various geographical locations. The temperature history of these exposed enclosures over a long period of time, along with the daily weather data from nearby weather stations, is contemplated to demonstrate the ability of PCMs in concrete to act as energy efficient building envelopes, and the cycling stability of PCMs in concrete under realistic exposure conditions.
This technology having been described in summary and in detail is illustrated and not limited by the examples provided herein. The FIGs provided herein provide results of the tests carried out in accordance with this disclosure, and certain FIGs are specifically referred to while describing the results below.
Water content (w/c)=0.45: Cement pastes and composite mortars. PCM employed Micronal 5008X (as supplied).
Volume fraction of PCM: 0-50%
Sealed Curing Conditions.
The latent heat storage capacity is shown in
The effect of PCMs on cement reaction rates is determined by isothermal calorimetry using pastes. The results are shown in
PCM additions do not influence rate of reactions;
PCMs do not alter reactions;
Range: 0-20% PCM (by volume).
The isothermal calorimetry response of certain compositions provided herein are determined. The results are shown in
This example measures the effect of compositions provided herein vis-à-vis temperature rise in cylindrical geometries. The results are shown in
This example demonstrates that PCMs show systematic heat absorption and release. See.
See,
Fracture toughness is determined using a two-parameter fracture model (Jenq and Shah. Journal of Engineering Mechanics, Vol. 111, No. 4, 1985, pp. 1227-1241) With increasing PCM dosage, critical crack tip opening displacements reduce at a lower rate than the fracture toughness. See,
This example demonstrates that the provision of PCM incorporated concrete compositions according to this disclosure is capable of comparable fracture toughness as that of conventional concretes. Such a property is desirable for alleviating cracking risk of a cementitious composition, See,
Drying shrinkage is measured as described in ASTM C157. The addition of PCMs does not influence shrinkage. PCM does not restrain overall shrinkage of paste phase. Thus, PCM addition does not alter deformability. In the case of a soft inclusion as relevant for this example, the continuous phase (cement paste), not the dispersed phase (PCM) is noted to control overall behavior.
Free deformation is measured under imposed thermal loads. Similar to moisture shrinkage, the PCM composition provided herein behaves like the plain cement paste. The results are shown in
Restrained thermal cracking is tested employing a dual invar setup. See,
Pastes are exposed to thermal cycles after 24 hours (sealed). Temperature loading at changing rates, is initially faster and then slower with time. PCM pastes shows clear effects of phase transition response, which becomes more pronounced at lower temperature change rates. The results are shown in
As used herein, a, an, or the includes reference to a plurality of thing or actions, unless the context indicates otherwise.
Every quantity and range(s) thereof are preceded by the term “about.” As the context indicates, about includes ±2%, ±5%, or 10% of a quantity.
This application claims benefit under 35 U.S.C. §119(e) of U.S. provisional application No. 61/600,463 filed on Feb. 17, 2012, the content of which is incorporated herein in its entirety by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/026489 | 2/15/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61600463 | Feb 2012 | US |
