Minimizing joint opening is crucial to ensure adequate load transfer across thejoints in ultra-thin whitetopping (UTW) pavement. Several UTW parking lot projects completed at the University of Illinois indicated that the initial joint cracks occurred at every 5 to 8 joints(for 4 by 4 ft panels). The result of this large crack spacing was wider openings at these initial crack locations and reduced load transfer. The primary objective of this theoretical thermal stress calculation for UTW was to determine if the initial crack spacing at early ages (e.g., 24 hours)can be approximately predicted for UTW sections, and if it is possible to promote additional cracks to propagate at early ages. The two types of thermal stresses considered are axial thermal stress due to uniform temperature change in the slab and curling stress due to temperature differentialthrough the slab thickness. Temperature profile data and laboratory elastic and fracture parameters are presented for several concrete mixtures at early ages. The analytical model coupled with the measured data revealed that 4 by 4 ft UTW panels will not crack at every saw-cut joint for the concrete mixtures and climatic conditions evaluated. Larger joint spacing, such as 6 by 6 ft, is sufficient but still may not propagate cracks at every joint. Initiating more joint cracks at early ages can be attained by higher stresses in the concrete layer (e.g., more slab restraint orlonger slab sizes), lower material fracture properties, or a deeper notch depth.
展开▼
机译:最小化缝隙开口对于确保超薄白面(UTW)路面中各个缝隙之间的负荷传递至关重要。伊利诺伊大学完成的几个UTW停车场项目表明,最初的缝隙裂缝出现在每5至8个缝隙处(4 x 4 ft面板)。较大的裂纹间距导致在这些初始裂纹位置处的开口变宽,并减少了载荷传递。用于UTW的理论热应力计算的主要目标是确定是否可以近似地预测UTW截面早期(例如24小时)的初始裂纹间距,以及是否有可能促进其他裂纹在早期扩展。所考虑的两种类型的热应力是由于平板中温度均匀变化而引起的轴向热应力和由于平板厚度之间的温差导致的卷曲应力。给出了几种早期混凝土混合物的温度曲线数据以及实验室的弹性和断裂参数。分析模型与实测数据相结合表明,对于评估的混凝土混合物和气候条件,4 x 4英尺的UTW面板不会在每个锯切缝处开裂。较大的接头间距(例如6 x 6英尺)已足够,但仍可能不会在每个接头处传播裂纹。在混凝土层中较高的应力(例如,更多的板约束或更长的板尺寸),更低的材料断裂特性或更深的切口深度可以在早期产生更多的接头裂纹。
展开▼