Abstract

The purpose of this study was to determine the suitability of sand and gravel deposits in Davis County, Utah, for use as aggregate in concrete. Davis County contains large quantities of sand and gravel which crop out in a narrow strip along the Wasatch Front for the entire length of the county. Most of the deposits are found in either Lake Bonneville terraces or in the Weber River delta. A total of 36 samples were obtained mainly from vertical channels cut perpendicular to bedding. The samples were sieved into 24 size grades using half-phi screens. Size grades ranged from plus 3.5 inches (plus −6.5 phi; plus 90.0 mm) to minus ASTM #325 (minus +4.5 phi; minus 0.045 mm). Data from the sieve analyses were reduced by a computer program which also calculated the first four moment measures; central tendency (mean size), dispersion (sorting), asymmetry (skewness), and peakedness (kurtosis). The petrographic analysis consisted of the identification of the main lithologic rock and mineral types found in the samples plus determination of Zingg shapes, visual sphericity and roundness, surface texture, degree of weathering, coatings, number of natural fractures, strength, amount of organic matter, and the chemical nature of the material.

The sand and gravel deposits of the northern part of Davis County are composed mainly of metamorphic and phaneritic igneous rock particles. While the deposits of the southern part contain a higher proportion of sedimentary and volcanic rock particles. Only very minor amounts of deleterious rock types (chert, shale, iron-rich rocks) are present in the deposits. The mean grain size of the particles is in the coarse fraction, with 50 percent of the samples having mean grain sizes in the pebble range. As a general rule, there is a very definite increase in the proportion of fine material from the southern portion of the county to the northern part. Almost all of the samples were very poorly sorted and most had skewness values indicating asymmetry toward the fine end of the distributions. Kurtosis values in 64 percent of the samples were in the platykurtic to very platykurtic classes, and one-third of the samples had leptokurtic values. All of the samples had moderate particle sphericity. Two-thirds of the samples contained more than 50 percent of disc- and/or rod-shaped particles, which are considered to be deleterious for use in concrete mixes. Ninety percent of the samples had mean particle roundness values in the subrounded to rounded classes. Weathering characteristics are not considered to be deleterious because most of the particles were only moderately weathered and only a minor percent of the particles had crumbly surface textures. Two samples had more than one-third of their particles with surface coatings, thus putting them in the potential deleterious class. Physical durability values placed one-third of the samples in the moderately hard class and the other two-thirds in the hard class. Three samples contained large amounts of organic matter, making them unsatisfactory for use in a concrete mix. Based on the parameters measured or tested for, the high percent of disc- or rod-shaped metamorphic particles in some samples is the main reason for material to be considered deleterious for engineering use. Therefore, the sand and gravel deposits in the northern part of the county are generally not as desirable for concrete aggregate as those in the southern part.