THE MYTH OF SAW-CUT JOINTS IN CONCRETE SLABS AND WALLS

This paper is concerned with the world-wide practice of providing shallow saw-cut joints or v-grooves at regular spacing, for structural purposes, in concrete walkway slabs, slabs-on-grade, and parapet walls. The primary purpose of this paper is to raise awareness among engineers that the practice is a myth and has no structural advantages, and for the engineers to think of a better and more positive/reliable approach to concrete crack control. The other purpose is to make aware the need for engineers to think and observe actual behavior of existing structures, and use that observation to improve future design, and not repeat unsound or useless practices. Elimination of useless saw-cut joints in future construction would save the whole world billions of dollars. The author demonstrates that the saw cuts have no structural impact by showing the pictures taken in New York of typical cracks seen on walkway slabs and parapet walls, and on garage floor slabs that were built with saw-cut joints. Note that this type of actual field observation is more representative than the crack observation on small concrete models tested in any engineering laboratories. For comparison, the author shows the examples of crack-free, maintenance-free garage floor slabs and parapet walls without any saw cuts that have been in service in Thailand for the past 30 years.

Shrinkage Cracking of Concrete Slabs-On-Grade: A Numerical Parametric Study

Industrial pavements are thin slabs on a continuous support subjected to restrained shrinkage and loads. The use of fibers as an alternative reinforcement to steel welded wire mesh and rebars is today an extensive practice for the reinforcement of concrete slabs-on-grade. Despite the widespread use of fiber reinforcement, the corresponding benefits in controlling cracking phenomena due to shrinkage are generally not considered in the design process of Fiber Reinforced Concrete (FRC) slabs-on-grade. The post-cracking performance provided by glass macro-fibers at low crack openings is particularly convenient in structures with a high degree of redundancy. Referring to service conditions, it is well known that concrete shrinkage as well as thermal effects tend to be the principal reasons for the initial crack formation in slabs-on-grade. A numerical study on the risk of cracking due to shrinkage in ground-supported slabs is presented herein. Special attention is devoted to the evaluation of the beneficial effects of glass fibers in controlling cracking phenomena due to shrinkage. The numerical analyses are carried out on jointless pavements of different sizes. Since shrinkage stresses in slabs-on-grade are considerably influenced by external constraints which limit the contractions, different subgrade conditions have been also considered.

Benefits of using amorphous metallic fibres in concrete slabs-on-grade

The effective utilization of pseudo-ductile materials like Fibre Reinforced Concrete (FRC) depends on the incorporation of suitable material parameters in appropriate design approaches. A design methodology has been developed for slabs-on-grade addressing various failure patterns, and giving a performance requirement as the design output. This opens up the choice of fibres, allowing the use of combinations of fibres to suit the service requirements. In this context, the current study explores the use of hybrid combinations of conventional steel fibres (SF) and a genre of corrosion-resistant amorphous metallic fibres (AMF) that have the ability to significantly enhance the flexural strength of concrete, even at relatively low dosages. It is shown that AMF, when used in combination with SF, results in a synergistic response with respect to toughness; mixes with 15 kg/m3 of SF and 20 kg/m3 of AMF exhibit about 50% higher characteristic flexural strength and more than double the characteristic equivalent flexural strength than the mix with 15 kg/m3 of SF alone, in the concrete considered here. Consequently, when FRC with a hybrid combination of fibres (AMF+SF) was considered in design, a significant reduction in thickness of slab was possible, in comparison to FRC with only SF.

A novel finite element method for designing floor slabs on grade and pavements with loads at edges

<p class="Abstractandkeywordscontent">In the present paper a methodology to design slabs on grade for industrial floors and pavements using bi-dimensional finite elements and integrating the subgrade in the design is presented. The suggested method to design slabs on grade for industrial floors and pavements has been called the Camero Finite Element Method. An example of an industrial floor designed to be capable of sustaining an infinite number of load applications (or a 50 years lifespan period) is here presented in order to be compared with the results of the Camero Finite Element Method, the PCA (Portland Cement Association), and the WRI’s (Wire Reinforcement Institute) simplified methods. In this example, an industrial floor is designed to be capable of sustaining an infinite number of load applications comparing the results of the Camero Finite Element Method and the simplified methods of the PCA and WRI. The industrial floor or pavement will be able to resist an infinite number of load applications if it is designed with the Camero Finite Element Method. On the other hand, if it is designed using the PCA and the WRI methods, it will last a few years (in this example, in one year period, the number of axle load applications is equal to the number of allowable repetitions). To conclude, if an industrial floor o pavement is designed with the Camero Finite Element Method, it will be able to sustain an infinite number of load applications (up to 50 years lifespan period).</p>