缓粘结预应力筋的试验研究

Experimental Study on Retard-bonded Prestressed Tendons

缓粘结预应力混凝土解决了后张有粘结和无粘结预应力混凝土自身无法克服的缺点,其核心问题是预应力筋周围的缓凝材料能否在预应力钢筋张拉前不凝结、张拉后逐渐凝结硬化。为此进行了缓粘结预应力筋的试验研究。通过大量的正交试验和理论分析,研制了一种能满足缓粘结预应力体系的缓凝砂浆,其初凝时间可以根据复合缓凝剂的掺量和养护温度从几小时到十几天任意调节,缓凝砂浆28d抗压强度达到35MPa以上。探讨了缓凝剂机理,通过手工方式制成了缓粘结预应力钢筋,并进行了模拟工艺试验。根据24片缓粘结预应力混凝土梁中52根缓粘结预应力钢筋张拉摩阻力的试验研究,得到了当缓凝砂浆的缓凝时间为15d,在第11天张拉预应力钢筋时的静张拉摩阻力、偏差系数k和摩擦系数μ。证明了这一新型预应力体系的可行性。

Retard-bonded prestressed concrete solves the problems that bonded and unbonded post-tensioned prestressed concrete can not overcome. The key problem of retard-bonded prestressed concrete is that the retarding materials around the prestressed tendons would not harden until the prestressed tendons are tensioned, so experimental study on retarding mortar is carried out. Based on a large number of orthogonal tests and theoretical analyses, the retarding mortar which meets the requirements of retard-bonded prestressed concrete is prepared. Initial setting time of retarding mortar may vary from several hours to 15 days at 5 - 35 ℃, which is due to quantities and average curing temperature. And its 28d compressive strength is above 35 MPa. Retarding mechanism is discussed. A retard-bonded prestressed tendon is made by manual work and the experiment that is to imitate the technology has been done. Based on 52 retard-bonded prestressed strands by manual work from 24 retard-bonded prestressed concrete T-beams, static friction drag, change factor k and friction factor u are obtained from the test when retard-bonded prestressed tendons are tensioned. It has been proved that this new prestressed concrete system is feasible.