Aaron Sakulich

Measuring Freeze and Thaw Damage in Mortars Containing Deicing Salt Using a Low-Temperature Longitudinal Guarded Comparative Calorimeter and Acoustic Emission

Deicing salts are often applied to the surface of pavements and bridge decks in the winter to melt ice, thereby improving safety for the traveling public. In this paper, the influence of NaCl deicing salt on freezing and thawing temperatures of pore solution and corresponding damage of mortar specimens were investigated. A low-temperature longitudinal guarded comparative calorimeter (LGCC) was developed to cool down a mortar sample at a rate of 2°C/h and to re-heat the mortar at a rate of 4°C/h. Heat flux during freezing and thawing cycles was monitored, and the temperatures at which freezing and thawing events occurred were detected. During cooling and heating, acoustic emission (AE) activity was measured to quantify the damage (cracking) caused by aggregate/paste thermal mismatch and/or phase changes. The results show that NaCl solution in a mortar sample freezes at a lower temperature than the value expected from its bulk phase diagram because of under-cooling. Conversely, the frozen solution in mortar melts at the same melting temperature as the bulk frozen NaCl solution. As the salt concentration increases, the freezing temperature is lowered. For samples containing more highly concentrated solutions, an additional exothermic event is observed whose corresponding temperature is greater than the aqueous NaCl liquidus line in the phase diagram. Damage also begins to occur at this temperature. For mortar samples saturated by solutions with 5 % and 15 % NaCl by mass, greater freeze/thaw damage is observed. The AE calorimeter developed herein is applicable for investigating damage behavior during freezing and thawing of different phases in pore solution (in mortars).

Experimental Apparatuses for the Determination of Pavement Material Thermal Properties

Degradation due to temperature fluctuation is the predominant deterioration mechanism affecting many asphalt and cementitious pavement systems. Reduced durability, in turn, limits the sustainability of a materials system: maintenance and replacement are almost always energy and resource intensive. As such, accurate quantification of the thermal properties of any given pavement material is necessary to determine durability and evaluate the effectiveness of novel technologies. Two somewhat inexpensive apparatuses have been developed for this purpose. The first, a Guarded Longitudinal Calorimeter (GLC), measures heat flow through a specimen sandwiched between standards of known thermal properties during either heating or cooling; from the measured heat flow data, many useful thermal properties (apparent thermal conductivity, etc.) can be obtained. The second device, a Solar Simulator, measures the temperature at different depths in multiple well-insulated specimens as they are heated or cooled by halogen lamps or cooled air blowers. The theory, construction, and operation of these devices will be detailed, and the results of analyzing pavement materials in each will be discussed.

Application of lightweight aggregate and rice husk ash to incorporate phase change materials into cementitious materials

Using phase change materials (PCMs) in buildings and pavements improves their thermal performance. However, PCMs cannot be directly added to cementitious media due to the interference of PCMs with hydration reactions. This study aims to evaluate the practicability of lightweight aggregate (LWA) and rice husk ash (RHA) to be used as PCM carrier agents in Portland cement-based mortars. The results show that LWA and RHA can absorb and contain liquids in their porous structures; and since these materials are compatible with cementitious media, they can be used as PCM carriers. However, a portion of the PCM may stick to the surface of the carriers or leak out of them and subsequently affect different properties of the binder. Incorporation of LWA presoaked in PCM decreased the compressive strength of the mortar by about 10%; however, when RHA was used as the carrier, the compressive strength was reduced by more than 35%.

Cool and Long-Lasting Pavements with Geosynthetic Reinforced Chip Seals

Pavements absorb a large amount of solar radiation. High pavement temperatures in warm climates cause problems such as rutting and accelerated aging of the mix, the urban heat island effect, and deterioration of air quality. This paper discusses, with models and experimental results, the concept of using an insulation layer, such as a geotextile, and aggregates with higher reflectivity in chip seals to reduce the conduction of heat through an asphalt pavement and increase the reflectivity of the surface. Reductions of temperature in the range of 8-10 °C were noted at the surface and 75 mm below the surface with the use of a 2.4 mm thick Petromat geotextile with chip seal. The study showed that a significant improvement in temperature reduction can be achieved with the use of a thicker insulation layer and/or an insulation of lower conductivity.

Insulating Pavements to Extend Service Life

Temperature fluctuations in asphalt pavements can increase the potential for rutting and cracking distresses. One way of countering this problem is to insulate a pavement from the extremes of air temperature and to also use a high reflectivity surface in warmer climates to reduce the absorption of solar radiation. This paper presents modeling and simulation results of the application of these concepts. Pavements with and without insulation layers were modeled in low temperature (Juneau, AK) and high temperature (Houston, TX) cities. A high reflectivity surface was also modeled in Houston. Temperature and solar radiation data for an entire year were analyzed for each city and the data corresponding to lowest and highest temperature (respectively) were utilized in the low and high temperature city pavement models. Results indicate that high temperatures were significantly reduced and that low temperatures were increased, depending on the thermal conductivity and thickness of the insulation layer. The presence of a highly reflective layer was also found to be very effective in reducing high temperatures in pavements. The positive effects of high temperature reduction on the service life of pavements was found to be significant, and the use of conventional materials of sufficient thickness was found to be feasible. Based on these findings, an ideal pavement section is suggested as one with an insulation layer near the surface, which could also serve as a moisture prevention layer; with a high reflectivity surface; and which is economical, durable, and capable of retaining its properties.

Effects of eccentricity and order of vibration modes on the inelastic seismic response of 3D steel structures

In torsionally coupled buildings, the total response of the structure is the result of the translational displacement of the storys center of stiffness and the displacement due to the roofs rotation. In structures with high eccentricity, the effect of the floor’s rotation in the total response is considerable. The order of vibration modes is another important parameter that changes the contribution of the different translational and rotational modes in the total response. To explore the effects of eccentricity and the order of vibration modes on the total response, a number of 3-D steel moment-resistant frames with 4, 8, and 12 stories, with different eccentricities and plans, were considered. The structures were subjected to bidirectional seismic inputs so that their peak ground accelerations were scaled to 0.4g, 0.6g, and 0.8g. Increasing the eccentricity of the structure increases the participation of rotation in the total response. Furthermore, in torsionally flexible structures, where the first or second mode of vibration is a torsional mode, the contribution of the floor’s rotation can be even greater. In some cases, the displacement of exterior columns is primarily the result of the floors rotation. This suggests that to efficiently dampen the seismic displacement of such structures, the rotational mode of the building should be controlled.