Pozzolans

There are several factors and test methods for evaluating the durability of concrete. In recent years a great deal of attention has been paid to research and development of relationships of these parameters for production of sustainable concretes: water penetration and Rapid Chloride Penetration Test (RCPT) methods which are most commonly used to evaluate the permeability of concrete are two of the most famous methods specified by BS EN-12390-8:2000 and ASTM C1202 respectively. Concrete surface resistivity (SR) test is also a suitable indicator for concrete penetration and chloride ion permeability. It is a nondestructive, simple, rapid and economical method that can also be used on site.

Rice husk ash was prepared as a pozzolana by a special process such that the final product conformed to engineering requirements in terms of physical and chemical properties, and the silica remained in an amorphous form with a minor amount of unburnt carbon. Results indicated that such a pozzolana can be produced with varying pozzolanic activity index depending on the degree of grinding and the burning temperature. The effect of rice husk ash content as partial replacement of cement on compressive strength and volume changes of different mixes is investigated. Test results showed that up to 40% replacement can be made with no significant change in compressive strength compared with the control mix. However, the effect on volume changes is within the limit specified in the American Standard.

Describes, with examples, two methods for selecting and adjusting proportions for normal weight concrete, both with and without chemical admixtures pozzolanic, and slag materials. One method is based on an estimated weight of the concrete per unit volume; the other is based on calculations of the absolute volume occupied by the concrete ingredients. The procedures take into consideeration the requirements for placeability, consistency, strength, and durability. Example calculations are shown for both methods, including adjustments based on the cheracteristics of the first trial batch.

Safe disposal of fly ash generated by coal-based thermal power plants continues to pose significant challenges around the world and in India in particular. Green structural concrete with 80% cement replaced by local Chinese fly ash has been recently developed to achieve a target characteristic compressive strength of 45?MPa. Such green concrete mixes are not only cheaper in cost, but also embody lower energy and carbon footprint, compared with conventional mixes. This study aims to adopt such materials using no less than 80% fly ash as binder in routine concrete works in countries like India with the commonly used lower target characteristic compressive strength of 30?MPa. It is achieved by the simple and practical method of adjusting the water/binder ratio and/or superplasticiser dosage. The proposed green concrete shows encouraging mechanical properties at 7?days and 28?days, as well as much lower material cost and environmental impact compared with commercial Grade 30 concrete. This technology can play an important role in meeting the huge infrastructure demands in India in a sustainable manner.

This study investigates the effect of partial replacement of cement with volcanic ash (VA) on the compressive strength of laterized concrete. A total of 192 cubes of 150mm dimensions were cast and cured in water for 7, 14, 21, and 28 days of hydration with cement replacement by VA and sand replacement by laterite both ranging from 0 to 30% respectively, while a control mix of 28-day target strength of 25 N/mm 2 was adopted. The results show that the density and compressive strength of concrete decreased with increase in volcanic ash content. The 28-day, density dropped from 2390 kg/m 3 to 2285 kg/m 3 (i.e. 4.4% loss) and the compressive strength from 25.08 N/mm 2 to 17.98 N/mm 2 (i.e. 28% loss) for 0-30% variation of VA content with no laterite introduced. The compressive strength also decreased with increase in laterite content; the strength of the laterized concrete however increases as the curing age progresses.

The construction and demolition (C&D) wastes constitute 25% of the solid waste generation in India. A large proportion of these wastes are disposed off as landfill leading to severe social and environmental problems. Environmental considerations are pushing the industry towards more sustainable practices which leads less energy intensive blended cements in construction. This paper examines the possibility of using the finely ground C&D wastes as cementitious material. The C&D wastes are categorised as processing waste and demolition waste. The processing wastes used in this study are saw dust ash and roof tile powder. The demolition wastes used for this study are concrete waste and laterite waste. The results obtained confirmed the pozzolanic activity of both processing waste and demolition waste.

Although history reveals that air lime mortars with added vegetable fat (ALVF) were used very often in the past, little knowledge about them survives to modern times. Little is known about the influence of fat addition on the mortars' durability, and some details about their manufacture and application are completely unknown. Even less is understood about the mechanisms that explain the behavior of ALVF-based mortars that also contain pozzolans. This paper reviews current knowledge about the characteristics of ALVF-based mortars in order to highlight questions that must be addressed in future research.

Non-destructive tests on building materials are increasingly adopted by engineers all over the world because these tests can be carried out without causing any damage to the original structures and there is virtually no limitation on time and location. Instead of using the conventional Ultrasonic test and Schmidt hammer test, the vibration test is suggested to assess the performance of concrete. In the vibration test, the resonant frequency of concrete, under the influence of other parameters, is examined. It is thought that the resonant frequency of concrete can be considered as a performance criterion. This paper describes a series of experiments to determine the resonant frequency of polypropylene fibre reinforced concrete. Within the test programme, three different curing conditions were simulated and addition of pozzolans, including pulverized fly ash (PFA) and silica fume (SF), to the concrete mix was studied. In order to find their combined effects, four different concrete mixes were designed and 24 concrete specimens were cast. Vibration tests were conducted and test results indicate that the resonant frequency may be affected by addition of polypropylene fibres, partial replacement of cement by pozzolans and curing condition.