EXPERIMENTAL RESULTS 



Retention of Chemical Solution in Aggregates 



After the lightweight, expanded shale aggregates were saturated 

 with a chemical solution under vacuum and then drip-dried (or washed in 

 mineral spirits) , they were found to have absorbed chemical solution to 

 the extent of about 25 to 30% of their dry weight. It was calculated 

 that the toxic chemical mixture constituted 10 to 12% of the weight of 

 the antifouling concrete made from the impregnated aggregate. 



Compressive Strength Tests 



The results of compressive strength tests [8] conducted on 2-inch- 

 cube concrete specimens containing chemically impregnated expanded shale 

 aggregates are presented in Table 2. For comparison, the table shows 

 that the compressive strengths of specimens of concrete made with sand 

 and gravel were approximately 6,000 psi. The compressive strengths of 

 specimens of concrete made from expanded shale aggregate impregnated 

 with water only (System 14) or with an aqueous solution of a toxic 

 chemical (Systems 3, 4, and 6) were approximately 5,000 psi. In nearly 

 all instances, values of approximately 3,500 psi were obtained for 

 concrete specimens made from aggregates impregnated with tributyltin 

 oxide (TBTO) (System 1), creosote (System 2), or with mixture containing 

 creosote, TBTO, and other toxic chemicals (Systems 5, 7, 8, 9, and 10). 

 Considerably lower values were obtained for the compressive strengths of 

 concrete made from aggregates impregnated with mixtures containing a 

 petroleum oil (Systems 11, 12, and 13). 



Rupture of the concrete cubes made from the expanded shale aggre- 

 gates occurred when the bond between the cement paste and the aggregate 

 was broken. None of the aggregate particles were observed to be sheared 

 or crushed. It is likely that a better bond was obtained between the 

 cement paste and natural aggregates than between the paste and the 

 expanded shale aggregates because the surfaces of the natural aggregates 

 are rougher and more irregular and the surfaces of the other aggregates 

 are fire-polished. The lower compressive strengths of concrete made 

 from the aggregates impregnated with creosote or other oils were probably 

 due to the formation of a thin oily layer over the surface of the expanded 

 shale aggregates which reduced bonding to the cement paste. 



Various techniques for removing the oily film on the surface of the 

 impregnated aggregates were tried. When the aggregates were drained on 

 a screen for a brief period, too much creosote or other oil was left on 

 the aggregate surface to permit satisfactory bonding to the cement 

 paste. The compressive strength of concrete made from the aggregate was 

 low. However, draining the aggregates for 24 hours removed sufficient 

 oil from the aggregate surface to permit satisfactory bonding to the 

 cement paste. A brief rinsing with a volatile solvent, such as mineral 

 spirits, noticeably cleaned the surfaces of the aggregates. In some 

 instances, but not in all, inadequate drying of the solvent before 

 mixing the concrete appeared to impair the strength of the concrete. 



