Experiences with sand-cement stabilization in road construction

At Hamburg, sand-cement stabilization (SCS) conseructed by the central-mixed (stationary plant) method is successfully used for frose-protection courses. The requirements applicable to these courses, which as a rule are 15 em thick, are based on those for cementbound sub-bases as laid down in the TVT regulations: degree of compaction ~98%, 28-day compressive strength 3 - 8 Nimm 20n Proctor specimens or 3 - l û N/mm'Z on lû cm diameter drilled c'or es . The SCSmaterials can be mixed and placed so as to achieve good and uniform qual~ty, as ~he average values from numerous projects carr~ed out ~n recent years show: degree of compaceion: X = 101.5 %, 5 = 1.31 ~ compressive strength (Proctor): X ~ 6.45 Nimm , s ,. 0.83 Nimm'}. co.mpressive strength (test core): ie z 6.52 ~/1m12 s • 1.6 Nimm In order to avoid open cracks the strengths of ses cour~es sho~l~ on no accoun~ exceed the 2 abovement~ oned l~m~ts of 8 Nimm and 10 Nimm resp~ctively Compressive strengths of between 3 and 6 Nimm should . be aimed at. Such sand-cement stabilized courses are frost-resistant. This has been established in tests on ll-year-old cores, but also in frost-resistance eests of increased severity. (12 times freezing of the water-saturated material). SCS materials can be placed and worked at air temperatures of about 20 Oc for periods of 5 - 6 hours without appreciable loss of strength. To avoid excessively rapid drying of the compacted layer~ it should be protected with a sprayed bitumen emu Ls i on (about 0.5 kg/m 2) or otherwise a bituminous Course be immediately laid over it. If the bituminous courses are' 12 em in total thickness, the ses course should be notched to a depth of about 5 cm at intervals of 5 m in the longitudinal and transverse directions. The admixture of coal fly-ash (loss on ignition' lSi.) has a favourable effect on ses materials so long as the ash content is ~ 40i.. Such mixes are frost-resistant even under severe conditions. The specimens should, however, be tested at an age of 60 days, not after a 28-day curing period. Higher values of the fly-ash content impair the frost-resistance and make it more difficult to install the ses material with proper surface regularity. The fine-grained ash brings about a more favourable microcracking behaviour: open cracks have hitherto not been observed even with jointless construction on large areas.