نشریه پژوهش های تجربی در مهندسی عمران
سال دوم شماره 2 (پیاپی 4، پاییز و زمستان 1394)

Recently، self-compacted concrete (SCC) is extensively used in civil projects because of their special fresh and hardened properties. These properties result from numerous parameters such as the paste content، the chemical composition of paste، the aggregate volume and aggregate grading. Although aggregates are inexpensive material but they can play an important role in concrete production. An increase in the proportion of aggregate particles directly result in decreasing cement paste content that is commonly used in filling up the voids and therefore، promote the efficiency of concrete particularly its mechanical strength and durability. This work attempts to introduce a method for approaching the proper aggregate grading with lesser void volume، by determining the influence of packing density of aggregates on the properties of SCC and by using uniformity coefficient together with coefficient of gradation in soil mechanics. The obtained results indicate that there is a logic correlation between packing density، uniformity coefficient، coefficient of gradation and void volume. Also، the results verify the effect of aggregate packing density on fresh and hardened properties of SCC.

Due to the wide spread using of concrete and concrete structures, as well as developing the use of additives in concrete, investigation in such area is very important. In this paper with the design and manufacture of high-strength concrete containing nano-silica, micro-silica, metakaolin and glass waste powder, the properties and effects of these materials when participate with cement type 2 reactions have been analyzed and criticized. Mechanical properties such as tensile strength and flexural strength at the age of 28 days, compressive strength at ages of 7, 28, 56 and 90 days and water absorption at the age of 90 days, have been examined. The obtained results indicate an improvement in the flexural strength of the majority of mix designs and also promote the compressive strength of mix designs containing nano-silica and metakaolin compared with control samples. The nano-silica, micro-silica, metakaolin and glass powder in all percentages caused to reduce water absorption relative to control sample. Due to the environmental and economic considerations associated with using glass powder in the aspect of long-term negative effects of this material on the compressive strength of concrete, its disadvantage is negligible.

The aim of this study is to investigate the settlement and stiffness of reinforced sand bed including soft pocket under rectangular model footing. The experiment initially was conducted on the model footing rested on sand bed. Then foam element was inserted in preset position for providing soft pocket condition. The foam distance from footing beneath, and the foam dimensions were examined as variable parameters. Results show that foam with B width create soft pocket condition at 2B distance of footing base and existence of soft pocket increase the footing settlement and decrease the stiffness and bearing capacity of foundation. By progressing the tests, the foam element was initially positioned in the sand bed and then the reinforcing elements were rested at the top of foam continued by loading the model footing. The bearing capacity, stiffness and settlement of sand bed were extracted from the load-settlement curves. The optimum values of reinforcing elements were obtained for reaching the ultimate bearing capacity. Results revealed that adding of reinforcement increased the bearing capacity and stiffness and decreased the settlement of foundation.

The most fundamental subject in applicable studies of fire in civil engineering is to evaluate fire load, which is affected by life style and consumable objects of the users. This subject has been considered more in countries like India, New Zealand, Canada and Finland, due to usage of structures sensitive to fire, like wooden structures. In this article, while defining the criteria for fire load evaluation and sampling from a number of residential buildings in Shiraz, the results of the researches done in other countries on fire load is compared with the results achieved in our country, Iran. Meanwhile various approaches of counting burning calories of different places and different household materials are explained. The results of this research are presented in different categories like the area of the residency, story number, sexuality of the users, application of the room and etc. plus a formula for evaluation of fire load in Iranian residential buildings is provided. This Formula, named after main writer of this article, Haji Beig Tehrani, is provided based on statistical studies, using different coefficients and the average fire load of a residential building in Iran. Concluding from this research, fire load in Iranian residential buildings is 541.8 Mega joules per square meter in average which is a high value, compared to other countries.

Recently, various researches have been undertaken on the high performance concrete (HPC). In order to obtain high strength concrete, certain materials and modern procedures are essential needs to get the result. Reactive powder concrete is a type of HPC that is under consideration of many recent works. The manufacture of HPC needs special materials that are not always accessible and applicable. However, in the present laboratory research regarding to the principles of reactive powder concrete manufacturing and using local available materials, it has been attempted to make HPC. In this view, numerous mix designs with different w/c and s/c proportions are made. The mix designs are added with and without standard amount of silica fume. Eventually, optimized and applicable mix design was obtained. According to reactive powder concrete manufacturing principles by using local materials, this type of concrete could be known as "modified reactive powder concrete".

To improve the strength of concrete, recently the use of different types of fiber is very common particularly in for civil engineering constructions. Most of the researches show that using the fibers will improve the compressive, tension and flexural strengths of concrete. The present work attempts to clarify the effect of different types of fiber on the mechanical strength of concrete. To achieve this aim, low amount of steel and glass fibers in mixes designed with two different rates of water to cement (W/C) ratios including 0.35 and 0.45 have been investigated. The steel and glass fibers have been used in concrete for 0, 0.30, 0.60 and 0.90 volume percent of concrete. For each ratio of water to cement: 21 cubic samples (10×10×10 cm) for compressive strength tests, 14 cylindrical samples (15×30 cm) for tensional tests and 14 prismatic samples (10×10×50 cm) for three-point flexural tests have been prepared. The laboratory results show that adding 0.30 to 0.90 percent steel fibers for concrete will increase the compressive, tension and flexural strengths in compare with normal concrete. Using the glass fibers between 0.30 to 0.60 percent by increasing the compressive strengths and by adding more fibers (more than 0.60 present), the compressive strengths will be decreased. In compare with normal concrete samples, by adding the glass fibers in the range of 0.30 to 0.90 percent of concrete volume, the tension and flexural strengths of reinforced concrete will be increased.

Silica fume as new supplementary cement material has several effects on initial mechanical strength and long term improvement in durability. In this paper, the impact resistance and mechanical properties of concrete mixed with silica fume are statistically investigated by preparing 288 specimens in three mix designs. The silica fume replaced 0, 7 and 14% of Portland cement by weight in mixed designs. Samples were made in different shapes including twenty cube, twenty cylindrical, and thirty-six 150×64-mm discs, casting from each batch for different test purposes. Cubic and cylindrical samples were used to determine the compressive strength and prismatic specimens were tested to obtain rupturing tensile. Also, cylindrical cutting specimens were subjected to the drop-weight test following the ACI committee 544 to determine impact strength of mixed concretes. Experimental data on the mechanical properties of different mixes indicate that silica fume improves mechanical properties and impact resistance while statistical analysis done based on these experimental tests showed the reduction of coefficient of variation values. In other words, adding silica fume improves statistical dispersion of data.