

Polymer-impregnated concrete (PIC) shows compression strengths of 20,000 <$ 

 psi, tensile strengths of 1,500 psi, and elastic moduli of 6.0 x 10 6 psi, 

 and, as compared to conventional concrete, an 80 to 90% decrease 

 in permeability and in creep. I? 5 J A major disadvantage of PIC is its lack 

 of ductility, but research is now being conducted to improve this prop- 

 erty. L J Other disadvantages are higher cost of PIC and lack of estab- 

 lished fabrication/construction methods and experience for large structures, 

 although such methods are currently under development. 



A newly developed dry casting technique that has not yet been field- 

 tested to any great extent yields concrete with a water-to-cement ratio 

 of 0.30 and thus has the potential for producing precast concrete members 

 of higher strength and lower permeability at competitive prices X J In 

 this method the ingredients are mixed dry, placed in the forms without 

 water, and compacted, after which water is introduced to fill the voids 

 by capillary action. 



The history of concrete is rich in novel approaches to improve con- 

 crete. Examples of successful innovations that are still practiced 

 include: vacuum removal of excess water from in-place concrete, pre- 

 packed techniques in which the coarse aggregate is initially placed in 

 forms and then intruded with grout' special compaction techniques^ and 



use of various concrete admixtures to reduce water, control setting 

 time, increase strength, durability, and workability, and otherwise im- 

 prove the engineering properties of the fresh and hardened concrete. L J 

 A new super-water-reducing admixture recently introduced to the industry 

 permits use of lower water-to-cement ratios while still providing a 

 workable concrete mix. 



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