In most cases, fiber reinforced self-compacting concrete (FRSCC) contains only one type of fiber. The use of two or more types of fibers in a suitable combination may potentially not only improve the overal properties of self-compacting concrete, but may also result in performance synergie. The combining of fibers, often called hybridization, is investigated in this paper for a cimentetious matrix. Control, single, two fibers hybrid composites were cast using different fiber type steel and polypropylene with different sizes. Flexural toughness tests were performed and results were extensively analysed to identify synergy, if any, associated with various fiber combinations. Based on various analysis schemes, the paper identifies fiber combinations that demonstrate maximum synergy in terms of flexural toughness.

The effects of lightweight aggregate type, content, and maximum size, as well as the water-to-binder ratio, on the fresh and Hardened characteristics of lightweight self-compacting concrete (LWSCC), were investigated. Fifteen LWSCC mixtures were prepared with varying proportions of LECA and scoria (100-0, 50-50, and 0-100%) and divided into two groups based on water-to-binder ratios and dmax values. The slump flow, T50, V-funnel flow time, and L-box were the fresh properties that were investigated, while the measurements of compressive strength, splitting tensile strength, flexural strength, modulus of elasticity, ultrasonic pulse velocity, and drying shrinkage were carried out in the Hardened state. The results indicated that higher scoria content generally declined fresh state properties and improved Hardened ones. An increase in dmax resulted in a reduction in the amount of superplasticizer needed to maintain the slump flow between 70 and 75 cm. The impact of the dmax on the mechanical characteristics of LWSCC was negligible. With increasing the dmax from 9.5 to 19 mm, the fc merely decreased by 7, 4, and 5% for S100-L0, S50-L50, and S0-L100 mixes, respectively. For ft, fr, and E, the decrease was between 3.2 and 0.6%. The correlation between compressive strength and splitting tensile strength was close to the CEB-FIP proposed relationship for conventional concrete, whereas the relationship between compressive strength and the modulus of elasticity was appropriately estimated using the ACI 318-19 suggested expressions. None of the proposed relations in ACI 209.2R-08 demonstrated adequate accuracy to predict the drying shrinkage of LWSCC at all ages.

Self-compacting concrete (SCC). was developed about four decades before since that time it has been used very scarcely due to a number of problems including: separation, lack of flowability and filling ability, high cracking potential, and thereupon low compressive and tensile strength. In this study, properties of SCC containing viscosity modifying agent, steel and polypropylene fibers were investigated. polypropylene fibers with dosages of 0. 1, 0. 125, 0. 20, 0. 150, 0. 185, 0. 205, and hook end steel fibers with volume fractions of 0. 5, 1, 1. 5, 0. 2 and 2. 5 were employed; fresh and Hardened SCC were examined. The results of the fresh concrete tests revealed that rise of the both fiber types reduces the slump flow and raises the T50 time. In the V-funnel test, the time shortened with polypropylene fibers up to dosage of 1. 25%, and then soars. Growing steel fibers elongate the time of the V-funnel test. Adding both types of the fibers reduces the passing ability of concrete in the L box test. Hardened concrete tests indicated that the compressive strength is falling by rising the dosage of steel fibers. The compressive strength at the age of 7 and 28 days improves up to the polypropylene fiber dosage of 1. 50% and then declines. At the age of 90 days, strength trend changes in dosage of 0. 1. Tensile strength grows as the both fibers increase. The crack test results show that the length and width of the cracks lower with the growth of the fibers. Adding steel fibers boosts the number of cracks.

There is a worldwide interest in using fibers of different types in concrete mixtures. In this regard, as the use of PET fibers has gradually increased during the last decade, this study aims to investigate the effects of PET fibers on the mechanical properties of Hardened concrete and the workability of fresh concrete. To this end, different contents of PET fibers (PC= %0, %0.5, %1 and %1.5) are added to a concrete mixture and the workability of fresh concrete samples are measured by the slump tests. Furthermore, the load-displacement behavior of the concrete samples is investigated in flexural and compression samples. Results of this study reveal that PET fibers can noticeably change the energy absorption of concrete samples, especially in flexural specimens.

The initial ages of heat created from the created temperature gradients are among the most destructive problems of large concrete structures, such as concrete dams, bridge bridges, massive foundations, and so on. Today, the use of cement supplements as a way to reduce thermal problems in these structures is very common. The subject of this research is Study the effect of substitution Silica Fume & Taftan Pozzolan. Instead of a percentage of cement weight On the thermal behavior and the process of obtaining the strength of Large concrete. For this purpose 11 mixed Plan Compounds 2 and 3 minor Silica Fume & Taftan Pozzolan With 0. 5 water to cement ratio & Cement cement 450 Kilograms per cubic meter was investigated. The results show that Replacement Silica Fume & Taftan Pozzolan The percentage of cement mainly reduces the maximum temperature of the mixture. Also replacement Taftan Pozzolan Reduced and Silica Fume Mainly increases the compressive strength of the early ages. Finally, the mix design has a replacement percentage 25% Taftan Pozzolan with 20% Silica Fume While increasing the strength of concrete by 25% (Compared to the control sample) Reduced the temperature by 7 °,C Which was introduced as a partial 3-point design.

Today, concrete is known as one of the most used building materials in the world. Silica fume and its products are now known as one of the best mineral additives in concrete. Silica fume is mainly used to improve the properties of Hardened concrete so when using Silica fume concrete properties after hardening usually more significant. But although various experiments have been conducted on the subject. But this thesis is considering other products of silica impact on the Hardened concrete properties have been investigated, including compressive strength, permeability and Thawing -freezing of Hardened concrete. Three mixing ratio is tested in the laboratory: 1- without additives and 350 kg per cubic meter of cement, 2- with 10% Silica fume powder and one percentage lubricant, 3- with 10% of the micro gel. Based on lab work conducted in the research and the gathering of results can be explained by the properties of Hardened concrete, the use of powder and gel of Silica fume increased compressive strength of 37.5 and 56 percent respectively. Water penetration rate, in the second ratio increase 50 percent and in the third ratio decreased 25 percent, compared to the first ratio. The results indicate the desirability of Silica fume gel long-term impact on the quality of Hardened concrete including its durability. While the silica fume powder, could adversely affect the permeability and Freezing-Thawing of concrete.

The cement paste properties as the matrix in concrete are of great importance in specifying its properties. Recent advances in concrete industry have highlighted the need for accurate knowledge about its nano-structure and components. To estimate the important mechanical properties such as Young's modulus, bulk modulus and Poisson’s ratio of the Hardened cement paste at the nanoscale, a comprehensive set of crystalline structures that represent the main Hardened cement paste constituents (CSH, CH, Ettringite, Hydrogarnet and monosulphoaluminate) is developed for Molecular Dynamics (MD) simulations. Five different force fields (COMPASS, COMPASS II, INTERFACE, Universal and Deriding) were used and compared with each other to be able to measure the mechanical properties of these compounds. Also, the properties of two types of C-S-H with high and low density were determined by using Mori-Tanaka method. Lastly, simulation results reported by the authors were compared with existing computational and experimental values. The results show that using molecular dynamics method was suitable in estimating mechanical properties of Hardened cement paste. These findings might be applied on larger scales and also multi-scale simulations.

The aim of this work is to investigate the influence of sodium oxide on properties of fresh and Hardened paste of alkali-activated blast furnace slag from Isfahan steel plant. The silica modulus (SiO2/Na2O) of activator was adjusted at 0.6 and a number of mixes were designed in such a way to contain different levels of sodium oxide including 1, 2, 3, 4, 5, and 6% by weight of dry slag. The most important physico-mechanical properties of the pastes including workability, initial and final setting times, 28-day compressive strength and efflorescence severity were measured. Suitable mixes were chosen for more studies including compressive strength at different ages, 90-day autogenous and drying shrinkages. According to the results, increasing the sodium oxide content of the mixes results in increased workability, reduced setting times, and higher compressive strength. The results confirm the possibility of achieving 28-day compressive strengths up to 27.5, 50.0 and 70.0 MPa for mixes with sodium oxide content of 1, 2 and 3 wt% respectively. The measured values for autogenous shrinkage were all less than 0.1% and SEM studies showed a significant decrease in pore sizes with increasing sodium oxide concentration from 1 to 2%.

Self-compacting concrete (SCC) due to several economical and technical advantages is increasingly used in construction industry. It can be improved on strength behavior when the fibers are added. Although the workability as a significant factor for this concrete must be maintained. This investigation experimentally evaluated the effects of steel and PET (polyethylene terephthalate) fibers separately on the properties of either fresh or Hardened SCC. Fresh properties of concrete have been investigated by slump flow, V-funnel and Lbox tests. Hardended properties were tested for compressive strength, splitting tensile strength, flexural strength, shrinkage and ultrasonic pulse velocity (UPV) tests. The results showed that 30 Kg/m3 Steel and 3 Kg/m3 PET fibers can be considered as suitable contents regarding to fresh and Hardened properties of SCC. However, the addition of PET fibers have caused a slight decrease in compressive strength.