تاثیر مصالح سنگی بر ظرفیت مخروط بتنی
Abstract
1- Introduction
2- State of the art
3- Experimental investigation
4- Results and discussion
5- Conclusions
References
Abstract
Recently, a large experimental campaign was completed that attempted to establish a link between petrography of the coarse aggregate, the concrete material properties and the system response in terms of concrete cone capacity. The investigation focused on three normal strength concretes having different coarse aggregate types (quartz, limestone, basalt) but otherwise similar mix design. All specimens of each concrete were cast from the same batch, carefully cured following three sets of curing protocols, and systematically characterized. The investigation comprised aggregate and concrete characterization, and structural tests performed at two ages on cast-in headed stud anchors under tensile loading. The aggregate characterization included the determination of Los Angeles coefficient, hardness and Young’s modulus. In order to characterize the concretes, standard compression and indirect tension tests, were performed together with fracture tests. The experimentally obtained material and structural data finally served for the evaluation of current predictive models in terms of concrete compressive strength or concrete fracture properties as well as a correlation study. Aided by photogrammetric analysis, the concrete cone shape was determined for each individual test and analyzed to uncover possible dependencies on the coarse aggregate type.
Introduction
Concrete is the fundamental structural material in the civil engineering industry. Over the last years it became one of the most used building materials. Fresh concrete can be cast easily into almost every shape. It is characterized by good mechanical properties (e.g. compressive strength) that are improving steadily with time due to ongoing hydration. Hence, it has almost unlimited applications in the modern construction industry. Fastening elements are an essential component of modern construction as they allow the connection of load bearing structural members and the installation of necessary equipment. The increasing age of our built infrastructure in combination with the rising awareness towards the environmental impact of the construction industry have further promoted the application of fastenings e.g. for strengthening and rehabilitation. Other trends such as fast modular construction also profit from recent advances in fastening technology. Depending on the specific properties of a chosen fastening system and the loading conditions a number of different failure mechanisms can occur, independently or in combination. One of the most critical failure mechanisms is described by the concrete cone capacity, i.e. the load necessary to rip out a fastening element by exceeding the load bearing capacity of the substrate material resulting in a cone like concrete break-out body attached to the fastening element. It is well know that concrete is a cementitious composite material – a mixture of cement, aggregate and water. Every component of the concrete mix design affects the properties of concrete. The aggregates take around 70–80% of the concrete volume and almost 90% of the total concrete weight. Consequently, they play also an important role in defining concrete thermal and mechanical properties. At early age, aggregates determine the workability, where the aggregate shape, surface roughness and type influence the interaction and bond between paste and aggregates [1]. The aggregate surface texture can be either rough or smooth, depending on the mineralogical type and the origin of the aggregates. Rougher surface results in a higher adherence and bond strength between the cement paste and the aggregates [2], while a smooth surface leads to better concrete workability during casting. In the past, many researchers investigated the aggregate effect on concrete properties, mostly on the concrete compressive strength. Delmar et al. [3] confirmed that at the same water to cement ratios, smaller sizes of aggregate lead to higher concrete strengths. On the other side, Vilane et al. [4] reported an increase of compressive strength with increasing aggregate size in a range of 9.5–19 mm.