including modified mixes with steel slag, taconite tailings, and granite; as well as other conventional mix designs. The following trends were obtained from the ...
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Figure 39 LWD modulus versus laboratory-measured moisture content values for subgrade soil (power) 56
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Figure 40LWD Modulus versus laboratory-measured moisture content values for GSB (power) As shown in Figure 40 the exponential regression model of moisture content and LWD Modulus for GSB layer (R²= 0.83). Here the correlation is higher than subgrade soil. In this plot Moisture content is taken on X-axis which is independent variable and LWD modulus that is Surface modulus ( ) Ͳܧ, is plotted on Y-axis. The regression equation is shown in Figure 39.
57
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Figure 41 LWD Modulus versus laboratory-measured moisture content values for WMM (Power)ent values for WMM (Power) As shown in Figure 41 is exponential regression (R²= 0.71) for wet mix macadam layer is lower than subgrade soil and GSB layer. From all three layers GSB is good correlated. The range of m/c in subgrade soil is from10% to 45%, for GSB layer is 8% to 25% and for WMM it was 6% to 14% only. It is because of presence of large aggregate in Wet Mix Macadam. Additionally, as the effect of moisture content is shown to be critically important when interpreting modulus-based test results, end-result specifications need to somehow account for this behaviour if these tests are to be used effectively for compaction control.
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CHAPTER SIX 6. CONCLUSION AND RECOMMENDATION 6.1. Conclusion. The above thesis work is an attempt to compare the conventional methods which is used in Highway construction and rehabilitation of road with NDG measurements which is a rapid tool to evaluate moisture content and density of the different layer of flexible pavement. A Regression analyses for bulk density indicated good correlations among subgrade (R²=0.80), GSB (R²=0.70), WMM (R²=0.759) and Asphalt Layer (R²=0.97). Similarly for moisture content R²=0.98, R²=0.91, R²=0.90 respectively for subgrade, GSB and WMM. The main purpose of the multiple-regression model was not to develop a predictive equation, but rather to investigate whether or not density measurements were related to any other variable in addition to the nuclear density measurements The t-test value is 1.998 which is at acceptance range the hypothesis for asphalt layer, that there is no difference between NDG readings and Core density results statistically. For practical field purposes, the nuclear method (direct transmission) for measuring bulk density and water contents is equivalent to other methods of bulk density measurement, when all procedures all carefully performed. From the field experience it can be said that larger volume of soil tested with the nuclear method compared to other conventional methods provides a more representative sampling of a soil mass. The sand-replacement test was found to have more intrinsic variability than the nuclear gauge method for bulk density measurement. The nuclear method of measurement for both density and water content is much faster than other methods. Assessment of in situ density and moisture content of compacted materials during highway construction requires portable, simple±to-use, non-destructive, economical and rapid tools without interference with construction process in order to effectively enhance construction 59
quality control of the entire earthwork. This study presents the evaluation of innovative QC tool called nuclear density gauge (NDG) which provides rapid and instantaneous measurement of density and moisture content and can improve the process of QA/QC in highway construction in India.
6.2. Recommendations
As per specifications given in manual they have recommendation errors such as chemical composition error, surface roughness error, depth of measurement and statistical precision of the gauge computed at the 68.3% confidence level. The nuclear gauge can be a very useful quality-control tool for measuring density and moisture content when used by experienced and skilled personnel. It contains radioactive source, which requires certified operator to run the gauge. It is intrusive method for soil testing and it takes time for preparing a test area prior to the measurement. It is applicable to 300mm depth only. Before using a nuclear gauge on a site for density testing, water content correction factors should be obtained for each soil type anticipated, as per manual of NDG. After performing nuclear measurements, the area tested should be exposed (with a spade) to inspect material tested and verify the water content correction factor to be used. The nuclear data may be regarded with a high degree of confidence if ASTM standard test procedures are followed. Sand-replacement tests require extreme care in calibrating the sand to obtain consistent results. Humidity and fines in the sand are special problems. Because more tests can be performed in a given time with the nuclear gauge, it has a higher likelihood of obtaining statistically valid results. A primary reason for preferring this testing method is its speed.
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6.3. Scope for future work For asphalt concrete dimensional core density method is done but by using ASTM 1188,it can be compared with it. The variation of measurements can be checked of NDG by setting different time domain, by using different soils, and also at different positions. It can also be correlated with different types of NDG by different company to compare the variations in measurement. Various methods of Indian Standards can be compared with NDG method such that rubber balloon, water displacement method etc. In this work thin layer and trench wall modes are not used so further both mode can be checked at various project and different locations. Further two parameters moisture and density can be related to different non-destructive methods such that LWD, FWD, DCP test and SSG to check the validity of instrument and effect of soil moisture content on its measurements.
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