Use of concept maps for problem-solving in engineering

This article presents a study on the use of concept maps as a learning tool for solving problems in engineering. Solving problems of structural analysis needs clear understanding of the fundamental concepts of the method and their links. Concept maps were used in lectures to explain the application of the concepts in solving problems and students were engaged in construction of concept maps before the actual calculations. Anonymous feedback was collected from students on the usefulness of concept maps in their learning. The responses show that the majority of the students found concept maps helpful in understanding the key concepts and their associations in solving problems. It helped students choose the right method from different options in solving a problem. Though the number of students constructing their own concept maps outside the classroom was relatively low, they wanted to see continued use of concept maps since it provoked the thinking process, and helped deep and meaningful learning. Thus, the use of concept maps facilitated student engagement in the classroom, helped solving problems and improved learning in the unit

Bond Strengths of Geopolymer and Cement Concretes

Geopolymer is an inorganic alumino-silicate product that shows good bonding properties. Geopolymer binders are used together with aggregates to produce geopolymer concrete which is an ideal building material for infrastructures. A by-product material such as fly ash is mixed together with an alkali to produce geopolymer. Current research on geopolymer concrete has shown potential of the material for construction of reinforced concrete structures. Structural performance of reinforced concrete depends on the bond between concrete and the reinforcing steel. Design provisions of reinforced concrete as a composite material are based on the bond strength between concrete and steel. Since geopolymer binder is chemically different from Ordinary Portland Cement (OPC) binder, it is necessary to understand the bond strength between geopolymer concrete and steel reinforcement for its application to reinforced concrete structures. Pull out test is commonly used to evaluate the bond strength between concrete and reinforcing steel.This paper describes the results of the pull out tests carried out to investigate the bond strength between fly ash based geopolymer concrete and steel reinforcing bars. Beam end specimens in accordance with the ASTM Standard A944 were used for the tests. In the experimental program, 24 geopolymer concrete and 24 OPC concrete specimens were tested for pull out. The concrete compressive strength varied from 25 to 55 MPa. The other test parameters were concrete cover and bar diameter. The reinforcing steel was 500 MPa steel deformed bars of 20 mm and 24 mm diameter. The concrete cover to bar diameter ratio varied from 1.71 to 3.62. It was found from the test results that the failure occurred by splitting of concrete in the region bonded with the steel bar, in both geopolymer and OPC concrete specimens. Comparison of the test results shows that geopolymer concrete has higher bond strength than OPC concrete. This suggests that the existing design equations for bond strength of OPC concrete with steel reinforcing bars can be conservatively used for calculation of bond strength of geopolymer concrete

Structural Behaviour and Design of Geopolymer Concrete Members

The worldwide production of concrete is on the increase in order to meet the increasing rate of construction. Since cement production contributes to the greenhouse gas emission, it is vital to develop alternative low-emission binders to reduce the carbon footprint of concrete. Fly ash based geopolymer is an alternative binder that has potential to reduce the CO2 emission of concrete production. It has been shown in different studies that the mechanical properties of geopolymer concrete are comparable to those of ordinary Portland cement (OPC) concrete. This paper describes the behaviour and design aspects of geopolymer concrete structural members. The design aspects presented in this paper are bond of reinforcing steel in pull-out and spliced bars in beams, beams in shear and flexure, and columns in uniaxial and biaxial bending. It is shown that the current provisions for OPC concrete can be conservatively used for design of reinforced geopolymer concrete members

Active learning by involvement in classroom

This paper presents a study on the effect of strengthened student involvement in an engineering classroom on their learning. The availability of online lectures has made learning more flexible. However, this can reduce the attendance of students in face to face lectures as students may excessively depend on the recorded lectures. Reduced attendance in lectures can significantly affect the deep and meaningful learning of units which is considered essential in an engineering course. Direct involvement of students in solving of problems was increased in the classroom activities in one part (part A) of a unit. The effect of strengthened student involvement on their learning was evaluated by looking at the attendance of students and their performance in the assessments. It was observed attendance increased and more students attempted questions of part “A” than the other parts of the examination paper. When performances in different parts of the unit were compared, it was found that lectures with strengthened student involvement improved their confidence on the topics. Thus, increased involvement or engagement of students in the classroom helped achieve deeper learning. Therefore, increased student involvement in lectures can help maintain high student attendance in classrooms when web-based lectures are also available for students to access at any time. The benefits of these web-based lecture systems can thus be maximised to promote deeper learning by involving students more in the classroom activities

Fly ash based geopolymer concrete: A review

Geopolymer binder is an emerging alternative of ordinary Portland cement (OPC) for concrete because of its comparable physical and mechanical properties shown in the recent studies. The current published literature indicates the prospect of geopolymer concrete for structural use. However, the overall performance and functionality under various environmental conditions has not yet been well documented. This paper reviews the works conducted on the fly ash based geopolymer concrete (FGPC) and summarizes its performance as a concrete material. The properties of FGPC are influenced by many factors such as the types and composition of fly ash (aluminosilicate source), final composition of chemical ingredients (alkaline activators), water to solid ratio and curing condition (temperature and relative humidity). Most of the previous studies were based on heat-cured or steam-cured samples. The implications of the current studies were analyzed to identify the critical factors holding back the wide application of FGPC. Further research areas for the improvement of FGPC were identified

Fire endurance of steel reinforced fly ash geopolymer concrete elements

As a new alternative to OPC, investigation into the fire endurance of geopolymer concrete is of utmost importance in order to ensure safety. Geopolymer and OPC concrete panels of 125–175 mm thickness containing a layer of steel mesh were exposed to fire for 2 h. Test results show higher heat transfer rate and less cracking and spalling in the geopolymer concrete specimens. The residual load capacity was between 61% and 71% for the geopolymer and between 50% and 53% for the OPC concrete panels. Thus, the reinforced geopolymer concrete elements demonstrated superior fire endurance than the OPC counterparts

Fracture properties of geopolymer concrete cured in ambient temperature

Geopolymer concrete (GPC) is a promising alternative of ordinary Portland cement (OPC) concrete. Recent studies indicate potential benefit of heat cured geopolymer concrete in structural applications. This study aimed at the fracture behavior of fly ash based geopolymer concrete cured in ambient temperature. Geopolymer concretes were prepared with mainly fly ash as the binder which was activated by a mixture of sodium hydroxide and sodium silicate solutions. Ground granulated blast furnace slag (GGBFS) was added up to 20% of total binder and amount of alkaline solution was varied to determine the effect on concretes subjected to ambient curing. Notched beam specimens were cast and cured in air at 16-22 oC and 70 ± 10% relative humidity. Three-point bending test was conducted using a closed-loop universal testing machine. The fracture energy values were calculated from the load-deflection curves of the test specimens by using the work of fracture method. The critical stress intensity factors of the specimens were also calculated. The load-deflection curves and the fracture behavior of different geopolymer concretes were compared. Generally, the fracture energy varied with the strength of the concrete. The fracture energy of concrete having slag in addition to fly ash was higher than that having only fly ash. Geopolymer concretes achieved higher fracture energy values as compared to OPC concrete of similar compressive strength

Improvement of Durability and Service Life of Concrete Using Class F Fly Ash

Durability is one of the primary considerations in designing concrete structures, especially when used in aggressive environment. Various supplementary cementitious materials (SCM) can be used to improve durability properties of concrete. However, the degree of improvement is dependent on the type of SCM and the mixture proportions of the concrete. In this study, Class F fly ash sourced from Western Australia was used as 30% and 40% of the total binder. The chloride diffusion properties of concrete containing fly ash were compared with those of control concrete. Fly ash concretes that were designed with adjusted water to binder ratio and total binder content to achieve similar 28-day compressive strength of the control concrete showed less chloride diffusion as compared to the control concrete. Simple deterministic service life estimation technique using the well known Fick’s law was applied to assess the service life of concrete mixes against the corrosion due to chloride diffusion. Early age properties were used along with certain selected parameters to predict the service life of concrete. Fly ash concretes resulted in higher service life than the control concrete when chloride diffusion was considered as the dominant form of attack

Fracture energy of geopolymer concrete

Use of fly ash based geopolymer as an alternative binder can help reduce CO2 emission of concrete. Effect of the geopolymer binder on fracture energy of concrete (GPC) has been investigated by testing both geopolymer and ordinary portland cement (OPC) concrete notched beams in accordance with the recommendations of RILEM TC 50 – FMC. The fracture failures of the GPC specimens were more brittle with relatively smooth fracture planes as compared to the OPC concrete specimens. Fracture energy of geopolymer concrete tends to be higher than OPC concrete for high compressive strengths