METHOD FOR MANUFACTURING ARTICLES FROM CONCRETE MIXES Russian patent published in 1994 - IPC

FIELD: civil engineering. SUBSTANCE: method involves placing and levelling the preheated concrete mix in the mold and compacting it partly by vibration. After placing the preheated mix, its temperature shall not exceed 60-65 C. Then cold mix is placed on top of it at a temperature of 10-30 C in a layer 20-40 mm thick. Next, temperature of heated mix is measured in the mold, a vacuum shield is placed on the levelled surface and the mix is vacuumized at a vacuum whose value is determined by the formulas P_р≅ Pмo

^ах=0,95(P_а-P_н), lgP_н= -2262,6/T+5,0607 where Pvр^f[ - maximum permissible vacuum in vacuum shield, MPa; P_а - atmospheric pressure, MPa; P_н - pressure of saturated steam at a mixture temperature T, MPa; T - temperature of heated mix placed into mold, K. In the first evacuation cycle the vacuum is increased smoothly. The duration of evacuation cycles is determined by the time of vacuum propagation through half the thickness of the article. Evacuation is alternated with periodical vibration at a vacuum of 0.01 - 0.03 MPa. Vibration is started at the end of each evacuation cycle 5 s before vacuum release and continued for 10-20 s. Vacuum is reduced from P_р to 0.01-0.03 MPa by blowing the vacuum shield with air through adjusting cock disposed on vacuum shield. EFFECT: lower energy expenditures, simplified manufacture and reduced time for vacuumizing and molding the articles. 1 tbl