In this papers, the punching shear strength of flat plate lightweight concrete slabs, using natural lightweight aggregates, is studied. In the experimental part of the study, six specimens of rectangular lightweight concrete slabs have been manufactured and tested. The strength of concrete and reinforcement varied in different tests. The slab dimensions and the area of reinforcing bars in slabs have been carefully designed so that the slabs failed due to punching shear. In each test, load and displacement were measured using a computer data acquisition system. The behavior of slabs, cracking pattern and the slab stiffness were studied from the test results. The experimental results have been compared with the provisions of different codes. The comparison shows that the BS-8110 Code estimates the punching shear of lightweight slabs most accurately. The slabs made of natural lightweight aggregates can be used in structures by providing good concrete mixture designs.    

In this research, the properties of structural lightweight aggregate concrete (LWAC) made of local lightweight aggregates in East Azarbaijan-Iran were investigated. Considering Iran earthquake zone, the weight of structures is of high importance. Reducing the weight of building using lightweight aggregates is one of the methods to decrease the harmful effects of earthquake on structures. In this study two different types of lightweight aggregates, Scoria and Pumice, provided from Azarbaijan-Iran, were used in concrete mixes. Mechanical properties of LWAC, including compressive strength, tensile strength, modulus of rupture, modulus of elasticity and stress-strain relationship were studied. In spite of NWC, the results show that at the same conditions, strength of aggregates is the main factor controlling the compressive strength of LWAC. Twenty-seven different concrete mixes with different 28 days compressive strengths varying from 24 to 51 Mpa were used in this study to measure the compressive strength, tensile strength, modulus of rupture, modulus of elasticity and strain at maximum stress which were compared with those of NWC. It was found that for the same compressive strength (24-51 Mpa) the modulus of elasticity of LWAC (10.92-18.77 Gpa) was less than that of NWC (17.53-28.31 Gpa) and tensile strength and modulus of rupture of LWAC was also less than NWC. The corresponding strain of the maximum stress in LWAC was found to be in the range of 2.55-3.78 mm/m, whereas for the same compressive strength, it was at range of 2.28-3.41 mm/m in NWC, this imply to lower modules of elasticity in LWAC compared with NWC.

Nowadays, the better performance of lightweight structures during earthquake has resulted in using lightweight concrete more than ever. However, determining the compressive strength of concrete used in these structures during their service through a none-destructive test is a popular and useful method. One of the most original approach of non-destructive testing to obtain of compressive strength of concrete used in structures is ultrasonic pulse velocity test. The purpose of this research is predicting the compressive strength of LWA concrete by proposing an accurate mathematical formulation. Many samples of lightweight aggregate concrete, made by expanded clay, have been produced and tested. After determining the actual compressive strength and indirect ultrasonic pulse velocity for each sample, a relationship was derived to estimate the compressive strength through Gene Expression Programming (GEP). The results show the presented equation shows high accuracy in predicting the compressive strength of LWA and the estimated outcomes have a considerable compatibility with actual samples.

Self-compacting concrete or SCC can be considered as the concrete of the future. The most important feature of self-compacting concrete is flowing under its own weight to fill the mould or framework completely, and also to create a dense and sufficiently homogeneous mix between the bars, without any need for vibration. But the excessive Liquidity of this concrete increases the hydrostatic pressure on the frameworks. So, decrease in the weight of self-compacting concrete could be lead to reducing the pressure on frameworks. It is also clear that decreasing the density of concrete has a significant effect on the reduction of the structure’ s weight and will lead to decrease in the size of structural elements. On the other hand, there are general concerns about the segregation of lightweight aggregates during transportation or placing. In this research, the ability of maintaining the homogeneity of the mixture and the mechanical properties of lightweight self-compacting concrete (LWSCC) made with common lightweight aggregates in the country including Scoria, Leca and Pumice, has been investigated on concrete columns, using the Semi-destructive and nondestructive methods. To do this, reinforced concrete columns made by self-compacting concrete were investigated using a semi-destructive core test to determine the compressive strength and impermeability. Nondestructive ultrasonic test at different heights of the columns was also conducted. The results showed that Scoria aggregate had generally better performance in self-compacting concrete compared to other lightweight aggregates.

A technical solution for the still existing problem of curing high strength concrete is proposed. The new method uses a blend of aggregates containing lightweight aggregates. The prewetted grains become a water supply at the disposal of the hardening and drying cement paste, allowing a continuous hydration which leads to improved properties of the concrete.

Volumetric change due to shrinkage affects performance of structural concrete thorough its service life. Prediction model that could be employed to estimate shrinkage after years will be beneficial for designer in analyzing such effect. Unfortunately, the existing prediction model for example ACI 209R-92 is developed for normal weight concrete. The validity of the model for estimating shrinkage of lightweight aggregate concrete (LWAC) is in question. This research is aimed to improve ACI 209R-92 model that will be applicable for predicting shrinkage of LWAC. For this purpose, measurement of shrinkage of LWAC up to 585 days on specimens with various curing periods were carried out. ACI 209R-92 model is utilized as starting point for the prediction of shrinkage of LWAC and then shrinkage half time value used in the model is modified to fit with the measurements. The proposed model is confirmed by the results of other investigators. It is shown that prediction of long-term shrinkage of LWAC could be improved when shrinkage half time used in ACI 209R-92 model is 65 instead of 35.

Lightweight aggregate concretes are widely incorporated in construction and development.This study, presents an experimental investigation on the properties of volcanic pumice lightweight aggregates concretes. To this end, two groups of lightweight concretes (lightweight coarse with natural fine aggregates concrete, and lightweight coarse and fine aggregates concrete) are built and the physical/mechanical and durability aspects of them are studied. The results of compressive strength, tensile strength and drying shrinkage show that these lightweight concretes meet the requirements of the structural lightweight concrete.Also, the cement content is recognized as a paramount parameter in the performance of lightweight aggregate concretes.