Commnon loadbearing effect of concrete pavement and cementbound sub-base

The combined load bearing action of the concrete pavement and the cement-bound sub-base (CRSB) has a favourable effect on the long-cerm behaviour of che road structure in the case of unreinforced concrete road slab construction wichout expansion joints. as has proved effective in Germany: - Because of che roughness of the CBSR surface and its connection to the concrete pavement (the slab) the dummy joints in the pavement open earlier and more uniformly. - Bond between the CBSR and che concreca pavement can be expected to last for some considerable time. It reduces the severity of the stresses in the oavement. Even after the bond has failed - chiefly in the vic~- oicy of the dummy joincs - a considerable frictional force continues to act. This friction likewise reduces tbe severity of the stresses in the pavement and also provides a substantial safeguard againsc undesirable displacement of the concrete slabs •. - The CRSB provides a uniform, temperature-indeoendent. stable (non-deformin~). rigid and adequately strong supporting layer. The defects which have sporadically been observed. and which in many instances have indeed been unjustifiably attributed to this form of construction, can be avoided by measures such as, for example: - It must be ensured that CBSRs do not 'lead a life of their own' due to temperature deformations. - CRSRs of 20 cm thickness and more (concrete subbases) should therefore, while the concrete is still very young, be notched longitudinally and transversely in order to prevent the formation of wide open cracks in the CRSB and random cracks in the pavement. The notches, like all the construction joints in the CRSB, should be aligned with the joints in che concrete pavement. - The surface strength of the CBSR and therefore ics durability in che vicinity of the joints is improved by adjusting the binder content to the aggregate and making it sufficiently high, by ensuring adequate uniformity of che mix. and by curing the surface of che CBSR for a sufficiently long time. - In the case of CBSBs which are impermeable co water the surface water which penetrates into the joints in the concrete pavement can be discharged by simole and effective drainage arrangements (e.g., shallow drains under the transverse joints of che hard shoulder) • - In the case of CRSBs which are permeable to water the underlying course (frost blanket) must also be sufficiencly permeable and water-discharging, so chat no build-up of water accumulating in this course and in the CBSB will occur. The above-mentioned measures are important in achieving durability, have been tried out in practice and have in part been incorporated in the new 'ZTVT' code for subbases.