Evaluation of the nuclear density/moisture gauge and study of some material properties affecting its performance for routine highway construction quality control in Kenya

Abstract

A study to assess the potentialities of the nuclear density and moisture(Troxler model 3411-B) for determining the in-situ density monitoring in Kenya is reported The field and prelimeinary laboratory gauge calibation were carried out with the sand replacement and oven-dry methods(on soils)and with asphaltic concrete (AC)cores.In the laboratory large mould compacted model samples were used in conjunction with nuclear gauge to obtain the density relationship of soil with count were rates.Subsequently,comparative density and moisture tests were done on eight soil types and two asphalt concrete pavements an four on-going road construction projects.The asphaltic concrete pavements were tested in respect of bulk density and voids content. The results of field tests show that the use of manufactures calibration curve can give substantial biased values for density and moisture determined by the conventional methods.The average standards errors relative to mean values were about +2(%moisture)for the latter and+80 kg/m for the former.These errors were more pronounced in materials containing iron and bound water as noticed in clayed soil) and in lime treated soils Systematic errors were reduced by recalibration of the gauge .The recalibration for each material encountered produced more accurate results for the moisture and density with standard deviation which were within the range 0.4-1.1(% moisture and 17-46kg/m^3 respectively.the investigation shows that after correction for hydrogen contained in water,density determination with the nuclear gauge were of even better accuracy. It is concluded that recalibration is necessary for every new material encountered.In addition,it is recommended that specifications should be drawn based on gauge long term tests to define clearly the acceptance of the gauge as a routine instrument for density and moisture determination on roads