The only difference between lightweight concrete and normal weight 

 concrete is that some or all of the "hard rock" sand, gravel, or crushed 

 rock is replaced by lightweight aggregate. Typically, the unit weight 

 of normal weight concrete is 150 pcf while lightweight concrete ranges 

 from 90 to 120 pcf. 



This study used expanded shale lightweight aggregate manufactured 

 under the brand name of Rocklite (Ventura, Calif.). Five aggregate 

 sizes - 1/2-inch, 3/8-inch, 5/15-inch, coarse sand, and fine sand - were 

 used (Figure 1). A sieve analysis for the aggregate is given in Table 

 1; Table 2 gives some physical properties of the aggregates. Of interest 

 are the data that show that the void volume ranged from 47% to 54% for 

 the aggregate sizes from coarse sand to 3/8 inch, respectively. The 

 internal structure of an aggregate particle is shown in Figure 2. 



Prior to mixing the regular lightweight concrete, the aggregate was 

 batched according to weight and then saturated with freshwater. In the 

 saturation procedure, air was evacuated from the aggregate for 20 minutes, 

 and then the aggregate was submerged in water for about 24 hours. At 

 this stage, the aggregate was placed in a pressure vessel and subjected 

 to 10,000 psi for 15 hours which gave assurance that saturation was 

 complete. 



It is highly unlikely that the hydrostatic pressure harmed the 

 aggregate. The void volume is interconnected and easily accessible to 

 water under pressure. A pilot study on saturation gave the data shown 

 in Figure 3. Soaking the aggregate after evacuation was not sufficient 

 to saturate the particles; however, as soon as 250 psi overpressure was 

 applied the aggregate became completely saturated in 48 hours. The 

 coarse sand and 5/16-inch aggregate showed the same behavior as that of 

 3/8-inch aggregate (see Figure 3) , except for different maximum water 

 absorption values. 



Polymer-Filled Aggregate (PFA) 



Regular lightweight aggregate was impregnated with polymeric mate- 

 rials to make PFA. Brookhaven National Laboratory performed the impreg- 

 nation. This organization has conducted similar work on impregnating 

 poor quality "hard rock" aggregate." 



The impregnation process used a monomer (liquid) to impregnate the 

 voids in the aggregate and then, by using heat, to polymerize the liquid 

 into a solid. The monomer system was, by weight, 83% methyl methacrylate 

 (MMA) , 5% trimethylolpropane trimethacrylate (TMPTMA) , and 12% polymethyl 

 methacrylate (PMMA) . The aggregate was oven-dried at 150 C for 24 hours 

 to remove free moisture from the pores. The aggregate was then placed 

 in a chamber and evacuated for 18 hours; at that point monomer was 

 introduced into the chamber. 



"Brookhaven National Laboratory. Report No. BNL-25396: Improvement of 

 wear-resistance properties of natural aggregates by materials impreg- 

 nating, by R. P. Webster and J. J. Fontana . Upton, N.Y. , Sep 1978, 

 34 pp. 



