Use of new road materials (industrial wastes) in mixes for sub-bases

The replacement of traditional aggregates (limestone) by crushed blastfurnace slag or LD steelmaking slag in lean concrete and in cement-stabilized hardcore was investigated. The effect of adding fly-ash to mixes of the conventional type was also studied. For mixes of equal composition (in parts by volume) and equal grading (by volume). the use of blastfurnace slag or LD slag has the following consequences: (I) Reduces compactability: the maximum compaction attained in the modified Proctor test is 77 - 83% instead of about 86%; (2) Has hardly any effect on the CBR (Californian bearing ratio) despite the lowered compaction; (3) Generally causes a slight reduction in the strengths attained at a given age; (4) Makes mixes possessing good durability (with regard to the action of water and of freezing/ thawing), except in the case of LD slag. which in the presence of water (even if the slag is well matured) is liable to result in the long-cerm complete breakdown of the stabilized mix. The addition of fly-ash improves the compactability of the mix. but ic makes the C~R more sensitive to variations in water content. A relatively major improvement in strength can be obtained as a result of the pozzolanic effects of the additive. In the case of binder-stabilized mixes for sub-bases some new types of road material offer by no means negligible economic and/or technical advantages (crushed slag, Ely-ash), whereas others are found to be highrisk materials when used injudiciously (LD slag).