abrasion has been underway for more than a century. The problem is com- 

 plicated because there are several different types of abrasion, and no 

 single test method has been found which is adequate for all conditions. 

 Abrasion can be classified into four types: 



(a). Wear on concrete floors due to foot traffic and light 

 trucking, skidding, scraping, or sliding of objects on the surface 

 (attrition) ; 



(b) wear on concrete road surfaces due to heavy trucks and 

 automobiles with studded tires or chains (attrition, scraping, and 

 percussion) ; 



(c) erosion in hydraulic structures such as dams, spillways, 

 tunnels, bridge abutments, concrete breakwaters, and piling due to 

 the action of abrasive materials carried by flowing water (attrition 

 and scraping) ; and 



(d) wear on concrete dams, spillways, tunnels, and other 

 water-carrying systems where high velocities and negative pressures 

 are present (generally known as cavitation erosion, which is 

 mainly the result of design and is not covered in this guide). 



To properly evaluate abrasion resistance, the type of concrete being 

 tested must be considered. If it is of the same mix throughout, the 

 abrasion resistance can be expected to be a direct function of the concrete 

 strength. If, however, metallic or other hardeners have been applied, the 

 time required for the abrasion apparatus to penetrate the hard surface must 

 be determined to properly evaluate the test results. 



(a) Factors Affecting Abrasion Resistance of Concrete . The 

 abrasion resistance of concrete is affected primarily by compressive 

 strength, aggregate properties, finishing methods, use of toppings, and 

 curing. 



Tests and field experience have generally shown that compressive 

 strength is the most important single factor controlling the abrasion 

 resistance of concrete, with abrasion resistance increasing with increase 

 in compressive strength. Compressive strength and abrasion resistance vary 

 inversely with the ratio of voids (water plus air) to cement. For rich 

 mixes, limiting the maximum size of the aggregate will improve compressive 

 strengths and result in maximum abrasion resistance of concrete surfaces. 



Proper finishing procedures and timing are essential if the quality of 

 concrete near the surface of a slab is to be as good as that for the 

 underlying section. Delaying the floating and troweling operations in- 

 creases resistance to abrasion. Another highly important ingredient in 

 wear-resistant, nondusting concrete surfaces is adequate curing (AC I 308- 

 71). One study showed that a surface cured for 7 days is nearly twice as 

 wear-resistant as one cured for only 3 days, and additional curing resulted 

 in further improvement. 



(b) Recommendations for Obtaining Abrasion-Resistant Concrete 

 Surfaces . The following measures will result in abrasion-resistant concrete 

 surfaces. 



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