Research On Ultra-high Strength Cementitious Composite And Products

New ultra high strength cementitious composite material(UHSCC) was the critical technique entitled to main point for sustainable development of construction industry, which emerged excellent durability that compression, bending, tensile,abrasion and corrosion resistance included. In allusion to a series of severe problem arised from HSC or UHSCC those low levels of hydration, vbrittleness, shrinkage,early crack, etc. UHSCC was consisted of river sand、fly ash、slag、silica fume, etc,in this paper. According to the current status of raw material in our country and the performance requirement of UHSCC that the preparative technique, the progression of physicial-machnical properties, the evolution of hydration capacity, drying shrinkage and the early crack resistance was scientifically investigated, of which revealed excellent comprehensive performance that was exploited for the preparation of UHSCC-manhole cover, which deflection was investigated that by the effect of the volume fraction of steel fiber,the thickness of manhole cover, reinforcement or not and the type of reinforcement material(reinforcing steel bar or fiber reinforce plastic),and the analysis of failed mode and economic effectiveness. The results show that:1. A larger difference of workability that alonged with the difference of admixture of UHSCC showed, which gave the good service in view of the cement was replaced patly by fly ash or slag, adversely silica fume and fly ash+slag+silica fume mixed.The workability of UHSCC was linearly reduced by the addition of steel fiber volume fraction, but the workability was improved with high efficiency water reducing agent companied. It suggested that the replacement ratio of cement by silica fume under 20% had taken consideration of the larger dosage of silica fume in tis paper.2. The compressive strength and flexural strength of UHSCC increased with the increase of age. With respect to the pure cement that compared with 28 d of standard curing, the compressive strength was increased by 3.5%, when the specimen was in certain of steam curing, adversely reduced by 12.1% under the hot water curing. The flexural strength was reduced by 1.4%~2.4% within the steam or hot water curing.The compressive strength and flexural strength of UHSCC both increased with the admixture mixed singly. Compared with 28 d of standard curing, the compressive strength flexural strength of UHSCC that fly ash or slag mixed singly was reduced by1%~12.1% and 15%~20% respectively. The compressive strength of UHSCC with silica fume mixed singly and triple-mixing was increased by 3.3% ~ 16.8%and14% ~ 21%, some increases and decreases exsited in the flexural strength that affected by curing regime that steam or hot water curing.Very smaller increase even lower with steel fiber volume fraction of 0 ~ 1.0%, but the adding value belowed28.4% that when the steel fiber volume fraction of 1.5%~2.0%.The best replacement material was slag and the best steel fiber volume fraction was 1.5% by the CT that the excellent interface was investigated.3. The variable law of early hydration of UHSCC by ray velocity that affected by admixture mixed, which experimented by an effective method, namely, Utrasonic Method. Compared with pure cement, micro-aggregate effect of admixture mixed expressed fully excellent properties.The analysis of Ca(OH) 2 and the law of pore structure was concerned with admixture mixed, curing regime and age of UHSCC: Ca(OH) 2 of the pure cement that was increase by the age, the percentage of Ca(OH) 2:steam curing>standard curing 28d>hot water curing. The progression of hydration was relation to admixture mixed, the lately content of Ca(OH) 2 was decreased with fly ash or slag mixed singly under the standard curing, which was embodied with the ability of the secondary hydration. The lower content of Ca(OH) 2 was compared with relative compressive strength and flexural strength of UHSCC of silica fume mixed sinly or triple-mixture, as a result of great effect of early strength of UHSCC with silica fume mixed. The percentage of Ca(OH) 2: pure cement>triple-mixture>fly ash>slag> silica fume under the steam or hot water curing.4. The total porosity of UHSCC with admixture was notly decreased, which revealed the ability of refining pore structure: slag> fly ash>silica fume>triple-mixture. Steam curing was superior to hot water curing, relatively.5. The drying shrinkage of UHSCC with admixture or steel fiber that was remarkably reduced by experiment, the rate of drying shrinkage was lowered largely,but a little with silica fume mixed or triple-mixture, which was grew insufficiently,when the steel fiber volume fraction was increased to 1.5%~2.0%. The risk of early crack was lowered greatly with fly ash mixed among the admixture. The effect of steel fiber on the crack resistance of UHSCC was advanced notably, and possessed the best crack resistance that the steel fiber volume fraction was increased to 1.5%.6. It is exploited that UHSCC manhole covers have been squeezed by the pressure of 500 t automatic pressure machine, which were obviously growth of carrying capacity that was concerned with the increase of steel fiber volume fraction and the thickness, reinforcement. The covers failed mode: bending and shearing. The basic performance of UHSCC manhole held approximately the 80% of cast iron manhole top, but the cost was only occupied 60%, even lower.