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39 to estimate angularity using WipShape. Both AIMS and LASS A total of 100 samples of natural silica sand and 100 samples use wavlets to describe angularity and texture (83, 86). of crushed sand were collected from the stockpiles of differ- ent ready-mixed concrete plants in Riyadh, Saudi Arabia. Also, the effects of silica and crushed sands--using different 2.6 TESTS FOR AGGREGATE PROPERTIES values of sand equivalents and passing a No. 200 sieve-- RELATED TO MOISTURE DAMAGE on water demands of mortar were investigated. A strong cor- 2.6.1 Introduction relation was found between the sand equivalent test and fine materials passing a No. 200 sieve for silica sand, whereas Moisture is a key factor in the deterioration of asphalt there was no correlation for the crushed sand. This indicates pavement. Factors that influence moisture damage include that the amount of fine materials in silica sand can be deter- aggregate, asphalt binder, type of mix, weather and environ- mined by either the No. 200 sieve or the sand equivalent test. mental effects, and pavement subsurface drainage. The pres- However, the sand equivalent test can be misleading for ence of plastic fines in the fine aggregate portion of HMA crushed sand. may induce stripping in the mix when exposed to water or Kandhal et al. (95) conducted a study to determine the best moisture. The following test methods are used to evaluate the aggregate test method that indicates the presence of detri- contribution of aggregate to moisture damage. mental plastic fines in the fine aggregate, which may induce stripping in HMA mixtures. Ten fine aggregates representing a wide range of mineralogical compositions and plasticity 2.6.2 Sand Equivalent Test characteristics were used. Their plasticity characteristics were evaluated by three test methods: sand equivalent test, plas- The sand equivalent test is a consensus aggregate property ticity index, and methylene blue value. Ten HMA mixtures specified in the Superpave mix-design method. The test was were made using a common limestone coarse aggregate, with originally developed in 1952 as a rapid field test by Francis these ten fine aggregates. AASHTO T283 (Resistance of Hveem, whose original work suggested that low sand equiv- Compacted Bituminous Mixture to Moisture Induced Dam- alents could indicate either clay or dust content. It is now age) and a Hamburg wheel-tracking device were used to eval- used to determine the relative proportions of plastic fines or uate the stripping potential of the ten HMA mixtures. Statis- clay-like material in fine aggregates. Excessive clay-like par- tical analysis of the aggregate test data and the mix validation ticles may cause the asphalt binder to debond from the aggre- test data showed that no significant relationship existed gate in the presence of moisture. Fine aggregate (passing the between sand equivalent test values and mixture validation 4.75-mm [No. 4] sieve) is placed in a graduated, transparent tests results. cylinder that is filled with a mixture of water and a flocculat- ing agent. After agitation and 20 min of settling, the sand sep- 2.6.3 Plasticity Index arates from the clay-like fines and the heights of sand and sand plus clay are measured. The sand equivalent is the ratio Plasticity index (PI) is being used by several agencies to of the height of the sand to the height of sand plus clay 100. measure the degree of plasticity of fines. PI is the difference Higher sand equivalent values indicate more sand and less between the liquid limit and the plastic limit of the material clay and silt. Minimum specified sand equivalent values for passing 425-m (No. 40) sieve. ASTM D1073 (Standard fine aggregate in HMA range from 26 to 60 (92). The Super- Specification for Fine Aggregate in Bituminous Paving Mix- pave method specifies a minimum requirement of 40 to 50, tures) and D242 (Standard Specification for Mineral Filler depending on traffic. for Bituminous Paving Mixtures) limit the PI of this fraction This test has the advantages that it is quick to perform; passing the 425-m (No. 40) sieve (including the mineral requires very simple equipment, which can be used with min- filler) to a value of 4 or less. Some states specify a maximum imal training or experience; and has given reasonably good PI for material passing the No. 200 sieve. A review of litera- results. However, there are some concerns about this test. In ture indicated no reported correlation between the PI and the 1997, Stroup-Gardiner et al. (93) evaluated the sand equiva- field performance of HMA (95). Precision data have not been lent test using 29 aggregates from a wide range of aggregate established for liquid limit and plastic limit tests, which are sources in Minnesota. Only 3 of 29 sand equivalent tests for based on subjective judgment and experience of the tester. individual stockpiles were less than 40%. The researchers found that sand equivalent test values were not sensitive to either the general mineralogy or the percentage passing the 2.6.4 Methylene Blue Test 0.075-mm sieve. There was no significant relationship between the sand equivalent test and mixture moisture sen- The test method titled "Determination of Methylene Blue sitivity (tensile strength ratio test results) or VMA. Adsorption Value of Mineral Aggregate Fillers and Fines" Alhozaimy (94) investigated the relationship between the is recommended by the International Slurry Seal Associa- sand equivalent and material finer than No. 200 sieve tests. tion (ISSA) to quantify the amounts of harmful clays of the