Appropriate energy efficient building envelope technologies for social housing in the Irish climate
Extensive dynamic thermal simulation parametric analyses have been undertaken of energy efficient fabric alterations to social housing in Northern Ireland culminating in priorities for deployment. Five ȁ8basecaseȁ9 simulation models were used to represent the predominant characteristics of the existing social housing stock. The majority of technologies studied provided annual space-heating energy savings of more than 10%. The variation of energy savings and economic performance across the basecases highlights the value of a dwelling specific approach to selecting energy efficient building envelope technology solutions for energy rehabilitation programmes. The paper further outlines a framework for prioritising appropriate energy efficient building envelope technological solutions for a large regional building stock, i.e. existing social housing stock in Northern Ireland, highlighting influential parameters. An energy efficient building envelope inter-technology ranking approach provides a method of comparison across the various different dwellings in the regional housing stock. Airtightness ranked consistently highest across the dwellings studied with some solar technologies performing better than more technologically mature solutions such as insulation.
Thermo-physical properties of nanostructured lightweight fiber reinforced cementitious composites
Abstract Cementitious materials are widely used for cladding of the building envelopes; however, they possess low thermal resistivity, low tensile strength and ductility which leading to cracking with time. It would be advantageous to improve thermal resistivity of lightweight cementitious materials whilst keeping their mechanical performance acceptable/reasonable. This study represents an extension to a work that has investigated the role of nano metakaolin (NMK) in enhancing the flexural strength of fiber reinforced cementitious composites (FRCC). An optimum composite of NMK – modified FRCC was determined. The aim of this study is to develop nanostructured lightweight fiber reinforced cementitious surface composites (NLWFRCC) with improved thermal properties and reasonable mechanical strength. For this purpose; white Portland cement (WPC) was partially replaced with different amounts of perlite ranging from 10% up to 70% by volume of cement then substituted by 10% nano metakaolin. Natural fibers were added by 2% by mass of binder. The bulk density, thermal conductivity, solar reflectivity, flexural strength, and capillary water absorption were determined in accordance to ASTM standards at 28 days of curing. The microstructure characteristics of the hardened NLWFRCC were investigated by scanning electron microscope (SEM). It was found that the density, thermal conductivity and fle x ural strength decrease with increasing replacements of cement by perlite, thermal conductivity at 70% perlite is 6.3 times less than the composite with no perlite (plain). Even at 70% Perlite; the developed NLWRFCC still retaining sufficient strength. Incorporating perlite into WPC, led to a significant enhancement in reflectivity especially in near infrared region; an increase of about 33% was obtained at 70% perlite.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.