مجله تحقیقات بتن ایران
سال پنجم شماره 2 (پاییز و زمستان 1392)

Reactive powder concrete (RPC), as a new type of ultra-high-performance concrete, has attracted a lot of attention in recent years. This type of concrete with a compressive strength of more than 150 MPa, has high packing density, very low permeability, superior durability and very high abrasion and corrosion resistance. Small steel fibers, used in RPC, cause the increase of flexural strength and ductility. In the present study, it has been tried to produce reactive powder concrete using the most suitable available materials in Iran. Also, the effects of different curing methods on the properties of RPC have been investigated. The results show that using the available materials together with steel fibers and conducting heat treatment, reactive powder concrete with compressive strength up to 160 MPa and flexural strength of 25 MPa was produced.

Use of the investigation on microstructure, have advantage that recognition on void and denser and durable and higher strength on concrete accorded. In this experimental study, investigated on compressive strength and velocity of ultrasonic waves and microstructure of interface transition zone on concrete with use of aggregates type of sillces, dolomite, limestone and granite on age of a polestar. By using of the Ultrasonic and Scanning Electron Microscope (SEM)set studied on microstructure on interface transition zone of concrete. The result shows the stuff of aggregate effect on compressive strength and so, the role of its on microstructures and thickness on interface transition zone. With increase of thickness of interface transition zone the velocity of ultrasonic waves on concrete decreased.

Objective of this study is to determine relation between compressive strength and tensile strength, and also special weight of concrete made with lightweight aggregate exploited fromthe existing mines in Kurdistan of Iran. For this purpose, mineralandchemicaladmixtures are used in concrete mix design and to produce lightweight concrete. The variables considered in the mix design are the ratio of compressive strength to concrete special weight, and the ratio of lightweight aggregate to the total volume of aggregate.An experimental study was carried out to examineeffect of the mentioned variables,after making and curingconcrete specimens. The results of the study show thatin most of cases, favorable compressive strength can be obtained by using the lightweight aggregate and constant amounts of cement and other materials in the mix design.

The current study is focused on gaining optimum concrete mixture design which contains nano-silica or mirco-silica, by employing different evaluation factors such as water to the cement ratio, cement grade and different age of investigation (7 and 28 days), using a robust predictive method that is called Taguchi. Nine mixture designs are optimized by Tguchi method to achieve maximum compression strength, maximum bonding strength between concrete and rebar and minimum water absorption. Obtained mixture designs are then employed in the laboratory and the results are investigated for the optimization process. In this study the XRD test is used in addition to mechanical concrete tests and permeability test in the macro scale. Obtained results show the reliability of the Taguchi method in the prediction of the concrete mixture design.

Nano-structurematerials recently attracted much scientific interest due to their superior performance. As well as concrete industry، according to its needs both in terms of strength and durability is one of the important users of nano structured materials. Therefore، concrete and mortar studies containing additive in nano scale is so important to development of new building materials. The aim of this study is to assess the self compacting mortars (SCMs) by using nano particles as a replacement of cement. In addition to reducethe amount of cement and to achieve the better workability، 25% fly ash was replaced in cement in all samples. Reduction of cement usage is a symbol of sustainable development and application of nano particles is a mark of nano technology helping in the same direction to make a brighter future. In this paper، the engineering properties of SCMs made by using of 1- 5% of SiO2، Fe2O3 and CuO nano particles are investigated. The fresh properties of mortar determined using mini V-funnel and mini slump flow tests and the hardened properties that determined by compressive strength، flexural strength tests at 3، 7، 28 and 90 days and water absorption test determined at 28 days. The results of experiments show the appropriate performance of the mentioned nanoparticles especially for SiO2 and CuO nano particles in improvement of workability، mechanical properties and durability of self compacting mortars.

The use of lightweight materials in construction industry reduces dead weight of structure and earthquake force acting upon it. On the other hand, the use of lightweight aggregates consider as a way to conserve existing natural aggregate mines. Self-CompactingConcrete (SCC) isa new type ofhighperformanceconcretes that flowsunderits own weight, passes through the reinforcements and fills all the corners of frameworks completely, The use of SCC is growing increasingly because of its great advantagessuch as eliminating the vibration of the concrete, reducing noise pollutionduring the construction time, having high workability and et. In this paper the effects of using two different artificial lightweight materials including light Expanded Clay Aggregates (LECA) and Expanded Poly-Styrene (EPS) on SCC are investigated. Fresh concrete requirement and the possibility of classification as lightweight self compacting concrete at hardened condition is determined.in order to evaluate structural lightweight self compacting beams, reinforced concrete beams were made of LECA and EPS and their design coefficient, bending capacity, modulus of rupture and deflection, compared with the normal weight SCC and also compared with the corresponding calculated values based on ACI 318.The results Shaw that the proposed relationships by ACI 318 code, are reliable when LECA is applied as lightweight aggregates, In this type of concrete, coefficient of lightweight concrete (λ) and bending capacity calculated by ACI 318 is smaller than corresponding experimental values, and calculated deflection is greater than experimental deflection. but the proposed design relationships by ACI 318 code, aren’t reliable when EPS is applied as lightweight aggregates, In EPS concrete, coefficient of lightweight concrete (λ), bending capacity and modulus of rupture calculated by ACI 318 is greater than corresponding experimental values.

In recent decades, to reach the lateral load resisting system which can satisfy a set of parameters, strength, hardness and flexibility, a lot of researches have been done. In recent years, in many countries, a new system called, steel plate shear wall (SPSW) has been used. Due to hardening and high strength, high energy absorption capability, speedy erection, economical and easy performance, the system has been used more in rehabilitation of existing steel buildings. While SPSW system can be easily integrated into existing steel frames, its suitability in concrete frames is still in the developmental stage. Currently on the behavior of reinforced concrete frame reinforced with SPSW research work has been slowly, because of have varied and complex behavior, researchers have always been interested in the use of concrete and steel together. In this study, first the numerical model has been verified by experimental results and then the behavior and the phenomenon of post-buckling in concrete frames reinforced with SPSW has been discussed. The results shows the suitable behavior of structure reinforced with SPSW and thereby it indicates load capacity, stiffness and energy absorption and flexibility of system increased. The actual drift ratio of floors using SPSW was also significantly reduced.

In this paper, the effect of pre-soaked local lightweight scoria fine aggregates on autogenous shrinkage, strength and transport properties of cement mortars is investigated. Different cement mortars with a constant water/cement ratio of 0.34 were prepared substituting normal fine aggregates by lightweight scoria fine aggregates with the same grading at five different volume fractions of 0%, 10%, 20%, 50% and 100%. Autogenous shrinkage, compressive and flexural strength, workability, pulse velocity, water absorption and sorptivity (rate of water absorption), were measured in all mortars and compared with reference specimen. It has been found that incorporation of pre-soaked lightweight scoria sand in cement mortars as internal curing agent can successfully control the autogenous shrinkage, but effects inversely on other properties (strength and transport properties) of mortars that should be significantly considered. It seems that an optimum use of pre-soaked lightweight scoria sand can modify all properties of mortars and concretes.