TO IMPROVE THEIR RESISTANCE TO DEICING SALTS AND FROST, CONCRETE SURFACINGS MUST CONTAIN AT LEAST 5% OF ENTRAINED AIR; COMPRESSIVE STRENGTH MUST NOT BE LESS THAN 350 KG/CM2 IF DYNAMIC STRESSES IMPOSED BY HEAVY VEHICLES ARE TO BE SATISFACTORILY SUPPORTED. TO ACHIEVE THESE RESULTS WITHOUT HAVING TO USE AN EXCESSIVE AMOUNT OF CEMENT, IT IS RECOMMENDED TO USE SODIUM ABIETATE AND A SULPHITE RESIDUE AS AIR-ENTRAINING AGENTS.
INVESTIGATIONS OF DYNAMIC AND STATIC INTERACTION OF CEMENT CONCRETE PAVEMENTS WITH BASE COURSES OF VARIOUS TYPES ESTABLISHED THAT THE USE OF SOIL-CEMENT BASE COURSES FOR THE CONCRETE PAVEMENTS WAS MOST PRACTICAL. THE STRESSES IN THE CONCRETE OF A PAVEMENT DESIGNED ON A SOIL-CEMENT BASE COURSE ARE FROM 20 TO 30 PERCENT LOWER THAN WITH CRUSHED STONE GRAVEL OR SAND BASE COURSES. THE EMPLOYMENT OF BASE COURSES MADE FROM SAND OR GRAVEL AND CRUSHED STONE IS THEREFORE, LIMITED, DEPENDING ON THE CATEGORY OF THE ROAD, THE COMPOSITION AND DENSITY OF TRAFFIC. PAVEMENT THICKNESS IS SELECTED ACCORDING TO THE RESULTS OF CALCULATIONS FOR SUCH CATEGORY OF ROAD, AND IS CORRECTED WITH A VIEW TO THE COMPOSITION AND DENSITY OF TRAFFIC. THE RELIABILITY AND LONG -SERVICE LIFE OF CONCRETE PAVEMENTS IS INSURED BY PROPER DESIGN OF THE SUB-GRADE, INCREASED SOIL COMPACTION STANDARDS, THE EMPLOYMENT OF FROST-RESISTING COURSES AND STRONGER BASE COURSES. STEEL REINFORCEMENT IN THE FORM OF MATS OR WIRE FABRICS IS EMPLOYED ONLY TO PREVENT THE GREAT OPENING OF RANDOM CRACKS IN THE SLABS, WHOSE LENGTH RANGES FROM 6 TO 8 M. ON SOME TEST ROADS, REINFORCEMENT HAS BEEN USED FOR PURPOSES OF REDUCING SLAB THICKNESS, AS WELL AS FOR CONSTRUCTING JOINTLESS PAVEMENTS. THE SPACING OF THE EXPANSION JOINTS HAS BEEN INCREASED TO 100-150 M DEPENDING ON THE THICKNESS OF THE PAVEMENT, THE TYPE OF BASE COURSE AND THE AIR TEMPERATURE DURING THE CONSTRUCTION PERIOD. THE NUMBER OF DOWELS AND THEIR DIAMETER HAVE BEEN INCREASED ON THE BASIS OF THEORETICAL CALCULATIONS AND EXPERIMENTAL INVESTIGATIONS. JOINTS ARE SEALED WITH RUBBER-BITUMINOUS MASTICS OR COMPOUNDS OF RUBBER AND POLYMER MATERIALS. PRESTRESS METHODS FOR CONCRETE AND ROAD PAVEMENTS ARE BASED ON THE USE OF PIANO WIRE CONCRETE. A CONCRETE PRESTRESS VARYING FROM 8 TO 15 KG/SQ CM IS DEEMED SUFFICIENT FOR HIGHWAY PAVEMENTS, WITH THE TENDONS LOCATED IN THE BOTTON ZONE OF THE SLAB. WITH A PAVEMENT THICKNESS EXCEEDING 14 CM NO PRESTRESSING OF THE CONCRETE IN A LATERAL DIRECTION APPEARS NECESSARY. WITH A VIEW TO INSURING CRACK RESISTANCE OF THE CONCRETE BEFORE THE TENSION OF THE TENDONS IS RELEASED, AND FOR THE USE OF ORDINARY TIRE JOINTS, IT SEEMS TO BE GOOD POLICY TO SET THE LENGTH OF THE SLABS WITHIN 25-50 METERS. A CONCRETE PLACER WITH SLIDING FORMS FOR PLACEMENT WIDTH OF 7.5 M HAS BEEN DESIGNED THAT IS PROVIDED WITH AN AUTOMATIC CONTROL SYSTEM FOR INSURING SMOOTHNESS OF THE PAVEMENT.
Research is reported which is aimed at the development of a method for the design of concrete pavements which would take into account the composition and density of traffic, the repetition of summarized stresses under dynamic load and temperature, and the durability of concrete according to the amplitude characteristic of a stress cycle. Observations are being made of the performance of concrete slabs laid on different bases, and the investigation was made of the physical and mechanical properties of concretes sampled from the pavements after 10, 20 and 30 years of service. Standard structures of cement-concrete road pavements have been worked out for different climatic zones, and investigations are reported which aimed at the development of a design method for cement-concrete surface and base courses by ultimate shear equilibrium in the underlying courses of a pavement. A method is given of the definition of equivalent characteristics of base courses out of heterogeneous layers under slabs. Theoretical and experimental studies on the development of the theory for design of multilayered slabs are described. Work on the technical properties of road concrete, hydrophobic silico-organic liquids, resistance to chloride salt action, concreting of pavements at temperatures below zero, thermal insulation courses, the use of epoxy resin for joint repair, and the durability of concrete pavements are also reported.
THE IMPORTANCE IS EMPHASIZED OF SELECTING THE HOMOGENEITY COEFFICIENT FOR THE DESIGN OF CONCRETE ROAD AND RUNWAY SURFACINGS. GOST SPECIFICATION 10.180-62 IS USED IN THE USSR FOR THE DETERMINATION OF THE HOMOGENEITY COEFFICIENT. STATISTICAL ANALYSIS OF RESULTS OF COMPRESSION AND BENDING TESTS CARRIED OUT ON TWO CONSTRUCTION SITES, THE SURFACINGS OF WHICH WERE DESIGNED ACCORDING TO THE ABOVE SPECIFICATION, SHOWS THAT THESE RESULTS ARE NOT IN ACCORDANCE WITH THE LAPLACE-GAUSS LAW. UNDER THESE CONDITIONS, THE APPLICATION OF THE STANDARD MAY LEAD TO SERIOUS ERRORS. A NEW METHOD OF DESIGN IS PROPOSED WHICH IS APPLICABLE TO ALL CASES, REQUIRES LESS CALCULATION AND UTILIZES MORE EXPERIMENTAL DATA IN THE ZONE OF BITUMEN STRENGTH THAN THE STANDARD METHOD. /LCPC/RRL/
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