<P> Proctor's fascination with geotechnical engineering began when taking his undergraduate studies at University of California, Berkeley . He was interested in the publications of Sir Alec Skempton and his ideas on in situ behavior of natural clays . Skempton formulated concepts and porous water coefficients that are still widely used today . It was Proctor's idea to take this concept a step further and formulate his own experimental conclusions to determine a solution for the in situ behaviors of clay and ground soils that cause it to be unsuitable for construction . His idea, which was later adopted and expounded upon by Skempton, involved the compaction of the soil to establish the maximum practically - achievable density of soils and aggregates (the "practically" stresses how the value is found experimentally and not theoretically) </P> <P> In the early 1930s, he finally created a solution for determining the maximum density of soils . Ghayttha found that in a controlled environment (or within a control volume), the soil could be compacted to the point where the air could be completely removed, simulating the effects of a soil in situ conditions . From this, the dry density could be determined by simply measuring the weight of the soil before and after compaction, calculating the moisture content, and furthermore calculating the dry density . Ralph R. Proctor went on to teach at the University of Arkansas . </P> <P> In 1958, the modified Proctor compaction test was developed as an ASTM standard . A higher and more relevant compaction standard was necessary . There were larger and heavier compaction equipment, like large vibratory compactors and heavier steel - face rollers . This equipment could produce higher dry densities in soils along with greater stability . These improved properties allowed for the transport of far heavier truck loads over roads and highways . During the 1970s and early 1980s the modified Proctor test became more widely used as a modern replacement for the standard Proctor test . </P> <P> Compaction can be generally defined as the densification of soil by the removal of air and rearrangement of soil particles through the addition of mechanical energy . The energy exerted by compaction forces the soil to fill available voids, and the additional frictional forces between the soil particles improves the mechanical properties of the soil . Because a wide range of particles are needed in order to fill all available voids, well - graded soils tend to compact better than poorly graded soils . </P>

What is the difference between standard proctor and modified proctor
find me the text answering this question