Energy Performance of Dynamic Roof Systems for Grid-Interactive Efficient Buildings

Building envelope elements are responsible for a significant share of the total building heat gains and/or losses specially for shell dominated structures. The development of high-performance thermal insulation materials and systems can be an effective approach to reduce heating and cooling thermal loads and even eliminate the need for air conditioning equipment. Instead of static insulation and cool roof materials, dynamic envelope systems can be beneficial to make buildings more adaptive to the outdoor environment and ultimately enhance their energy efficiency and sustainability. The research work outlined in this dissertation aims at investigating the energy performance of dynamic roof technologies applied to residential and commercial buildings. In particular, two main technologies are evaluated including switchable insulation systems and dynamic cool roofs. Both technologies are assessed individually and in combination with other adaptive envelope systems with the ability to adjust their thermal and optical properties based on simplified and optimal control strategies. Moreover, an extensive cost-benefit assessment has been carried out for switchable insulation systems when applied to retrofit attics of existing US residential buildings. The analysis results indicate that roof integrated switchable insulation systems can be highly effective in reducing both heating and cooling energy end uses for both residential and commercial buildings even when simplified controls are deployed. The energy efficiency and peak demand shifting benefit of the adaptive building envelope systems can be enhanced through optimized controls especially when precooling strategies are considered. Specifically, the analysis revealed that implementation of adaptive envelope systems can achieve nearly net zero energy operation for both residential and commercial buildings.</p

Effect of sulfate concentration and associated cation type on chloride-induced reinforcement corrosion

Effect of sulfate concentration and associated cation type on chloride-induced reinforcement corrosio

Chloride-induced reinforcement corrosion in blended cement concretes expores to chloride-sulfate environments

This paper reports the results of a study conducted to investigate the influence of sulphate concentration and associated cation type on chloride-induced reinforcement corrosion in blended cement concretes. Reinforced concrete specimens were exposed to chloride plus sulphate solutions for a period of 1200 days. The exposure solutions contained a fixed concentration of 5% sodium chloride and the sulphate concentration was varied from 0 to 4% SO4 2 . The effect of cation type associated with sulphate ions, namely Naþ and Mgþþ, on chloride-induced reinforcement corrosion was also evaluated. Reinforcement corrosion was assessed by measuring corrosion potentials and corrosion current density at regular intervals. The results indicated that the presence of sulphate ions in the chloride solution increased the corrosion current density, but no significant effect on the time to initiation of reinforcement corrosion was noted. Further, the corrosion current density increased with increasing sulphate concentration and the period of exposure. The corrosion current density on steel in the blended cement concrete specimens was much less than that in the plain cement concrete specimens, indicating that the corrosion resistance of blended cements was much better than that of plain cements. The cation type associated with sulphate ions did not significantly influence either the initiation or rate of reinforcement corrosion

Long-term effect of sulfate ions and associated cation type on chloride-induced reinforcement corrosion in Portland cement concretes

This paper reports the influence of sulfate concentration on chloride-induced reinforcement corrosion in Portland cement concretes (with C3A varying from 3.6% to 9.65%). The concrete specimens were exposed to mixed chloride and sulfate solutions for a period of 1200 days. The chloride was fixed at 5% NaCl for all solutions, while the sulfate concentration was varied to represent that noted in the sulfate-bearing soil and ground water. The study included an assessment of the effect of cation type associated with sulfate ions, namely Na+ and Mg2+, on chloride-induced reinforcement corrosion, an important factor that has received little attention. Reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density at regular intervals. The results indicate that the presence of sulfate ions in the chloride solution did not influence the time to initiation of chloride-induced reinforcement corrosion, but the rate of corrosion increased with increasing sulfate concentration. Further, the rate of chloride-induced reinforcement corrosion in the concrete specimens exposed to sodium chloride plus magnesium sulfate solutions was more than that in the concrete specimens exposed to sodium chloride plus sodium sulfate solutions

Effect of cement alkalinity on pore solution chemistry and chloride-induced reinforcement corrosion

This paper reports the results of a study conducted to evaluate the influence of cement alkalinity on the pore solution chemistry and chloride-induced reinforcement corrosion in ordinary and sulfate resisting Portland cement concretes. To evaluate the influence of cement alkalinity on the pore solution chemistry, cement paste specimens were prepared and admixed with fixed quantity of sodium chloride and various dosages of alkalinity (in the range of 0.4 to 1.4% Na2O equivalent). The pore solution was extracted and analyzed to determine the OH-, Cl- and SO4 -- concentrations. The influence of cement alkalinity on chloride-induced reinforcement corrosion was also assessed by measuring corrosion potentials and corrosion current density at regular intervals. The results indicated that the OH-, Cland SO4 -- concentrations of the pore solution increased with increasing alkali content of the cement. Further, the Cl-/OH- ratio decreased with increasing alkali content up to 0.8% Na2O and then increased with a further increase in the alkalinity. Furthermore, an improvement in the corrosion-resistance of the SRPC and OPC concrete specimens was noted with increasing alkali content of cement. However, the highest improvement was noted when the alkalinity was 0.8% Na2O equivalent

Influence of cement composition on concrete durability in chloride-sulfate environments

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