DISCUSSION 



Optimum (and practical) curing procedures as well as optimum cement 

 content are vital to achievement of adequate expansion. Adequate expan- 

 sion to overcome (compensate for) shrinkage will also "prestress" the 

 panel; the magnitude and benefits of this concrete precompression must 

 be determined on a life-cycle basis before the procedure can be economi- 

 cally justified. The life-cycle effects of the wet mortar on the thermal 

 conductivity of the "sandwiched" polyurethane foam must also be determined. 

 Since structural strength of the W-Panels has been established by ICBO, 

 only a few tests of expansive concrete panels will be needed to verify 

 their strength. 



CONCLUSION 



Based on results shown in Figure 4, use of expansive cement mortar 

 to prevent shrinkage cracking in the W-Panel is a technically viable 

 concept. Embeddable resistance strain gages are more reliable for 

 measuring strain in the W-Panels than a mechanical strain gage used on 

 embedded screw-type reference points. 



RECOMMENDATIONS 



To reduce life-cycle and energy costs of new concrete structures by 

 up to 30% by using expansive concrete panels with insulation at mid- 

 thickness to produce crack-free sandwich-type walls and roofs, the 

 research program outlined below is recommended. 



1. Experimental sandwich wall and roof panels, containing insulation 

 at mid-thickness, should be made with shrinkage-compensating expansive 

 cement concretes to eliminate shrinkage cracking. Optimum amount of 

 expansive cement, optimum curing method, and optimum panel thickness 

 should be determined. Volume changes (potential to crack from shrinkage) 

 strength, thermal conductivity, and density should be determined on 

 experimental wall and roof panels. In addition, the optimum method of 

 placing the mortar (plaster) should be developed (shotcrete, pumping, 

 etc.). 



2. Design procedures, including tables and charts, should be developed 

 for energy-efficient expansive concrete wall and roof panels. 



REFERENCES 



1. "Expansive cement concretes--Present state of knowledge," Journaj. o- 

 the American Concrete Institute, Aug 1970, pp 583-610. 



2. "Recommended practice for the use of shrinkage-compensating concrete,' 

 Manual of Concrete Practice, Part 1. American Concrete Institute, 1977. 

 (ACI 223-77) 



3. International Conference of Building Officials, Research Committee 

 Recommendation Report No. 2440, Jul 1978. 



