Jahangir Mirza

Laboratory and field performance of polymer-modified cement-based repair mortars in cold climates

Abstract The results of an ongoing test program to evaluate the performance of polymer-modified cement-based mortars for repairing surfaces of concrete structures up to a depth of 75 mm (3 inches) damaged due to exposure to cold climates are presented. Twenty-five selected commercially available polymer-modified products, seven containing styrene butadiene rubber (SBR) and 18 containing acrylics were evaluated. They were compared with those of a pure cement-based mortar containing 8% silica fume by weight of the cement, with a water/cementitious materials (cement+silica fume) ratio (W/CM) of 0.31. All of the mortars were subjected to thermal compatibility with base concrete, drying shrinkage, permeability, abrasion-erosion resistance, bond strength, compressive strength and freezing and thawing cycling tests. The thermal compatibility with the base concrete at temperatures from −50 to +50 °C was used as a pre-selection test. This paper also presents the satisfactory performance of the three best selected polymer-modified cement-based mortars (included in the 25 mortars), after 6 years in service on two operating spillways of a dam in a severe cold climate.

Basic rheological and mechanical properties of high-volume fly ash grouts

Abstract Soil, rock and oil-well grouting require enormous amounts of cement and are therefore good examples of areas where high volumes of fly ash could replace cement partially to produce low-cost, environmentally friendly and durable grouts. This paper presents the results of the particle size distribution, three rheological properties (flow time, bleeding and setting time), and five mechanical and strain properties (compressive strength, shear bond strength, modulus of elasticity, Poissons ratio and drying shrinkage) of high-volume fly-ash (HVFA) grouts (cement replacement by fly ash of over 55% by weight), with and without superplasticizer (SP) and/or anti-washout agent (AWA). Rheological properties are reported for eight water–cementitious materials (cement+fly ash) ratios (W/CM), ranging from 0.4 to 1.3, whereas mechanical and strain properties of hardened grouts are given at W/CM of 0.5, 0.55 and 0.65. The effects of SP and AWA on the flow time of low-W/CM grouts and the stability of high-W/CM grouts were investigated. The results indicate that the addition of fly ash in cement grouts reduces the flow time, improves stability, reduces drying shrinkage, and attains similar compressive and shear bond strengths as pure cement grouts at later ages. Moreover, when SP is used for low-W/CM grouts, the latter destabilizes, and in those cases AWA should be used.

Reviews on Corrosion Inhibitors: A Short View

A range of numerous corrosion inhibitors, viz. organic molecules with hetero atoms and π-electron clouds, inorganic salts and plant excerpts likewise their corresponding phytoconstituents were reported with success for metals in different corrosive media. Various literature reviews related to corrosion inhibitors have been reported by many authors based on their application, classification, and inhibition mechanism. A short view of all these reviews is summarized in this manuscript. Various aspects of corrosion inhibitors as well as their recent trends and advancement are also discussed.

Thermal Behavior of Cylindrical Buckling Restrained Braces at Elevated Temperatures

The primary focus of this investigation was to analyze sequentially coupled nonlinear thermal stress, using a three-dimensional model. It was meant to shed light on the behavior of Buckling Restraint Brace (BRB) elements with circular cross section, at elevated temperature. Such bracing systems were comprised of a cylindrical steel core encased in a strong concrete-filled steel hollow casing. A debonding agent was rubbed on the cores surface to avoid shear stress transition to the restraining system. The numerical model was verified by the analytical solutions developed by the other researchers. Performance of BRB system under seismic loading at ambient temperature has been well documented. However, its performance in case of fire has yet to be explored. This study showed that the failure of brace may be attributed to material strength reduction and high compressive forces, both due to temperature rise. Furthermore, limiting temperatures in the linear behavior of steel casing and concrete in BRB element for both numerical and analytical simulations were about 196°C and 225°C, respectively. Finally it is concluded that the performance of BRB at elevated temperatures was the same as that seen at room temperature; that is, the steel core yields prior to the restraining system.

Mechanical Properties and Freezing and Thawing Durability of Polypropylene Fiber-Reinforced Shotcrete Incorporating Silica Fume and High Volumes of Fly Ash

This paper describes the materials used, mixture proportions, mixing and shotcreting operation, and properties of the fresh and hardened polypropylene fiber-reinforced shotcrete incorporating silica fume and high volumes of fly ash. The polypropylene fiber-reinforced high-volume fly ash shotcrete produced had satisfactory workability, mechanical properties, and resistance to freezing and thawing cycling. The shotcrete containing silica fume had negligible rebound compared with that without silica fume. The incorporation of fly ash and silica fume improved the workability of the fresh shotcrete, and this resulted in lower operating pressure for the shotcreting. The use of polypropylene fibers up to 0.5% by the volume of the shotcrete did not affect significantly the compressive strength, and the shotcrete incorporating both fly ash and silica fume bonded well to the base concrete. The fiber-reinforced shotcrete showed satisfactory performance after 300 cycles of freezing and thawing with a durability factor greater than 80, even though the air contents were relatively low and the spacing factor was relatively high.

Performance of Pakistani volcanic ashes in mortars and concrete

Two Pakistani volcanic ashes, VA1 (as is and calcined) and VA2 (as is), were incorporated into mortar cubes, concrete cylinders, and concrete beams as a partial substitute for ordinary Portland cement (OPC), and were studied in detail. The X-ray diffraction patterns showed that both ashes possessed crystalline as well as amorphous phases. The pozzolanic activity index (PAI) of VA1 at 7 d was below 75%, whereas it was 80% at 28 d. The pozzolonic activity indices in OPC mortars containing VA2 were much higher than those for VA1, both at 7 and 28 d. In mortar cubes and concrete cylinders, approximately the same compressive strengths were observed in samples containing 100% cement as in those incorporating a 10% replacement of cement by either VA1 or VA2. Mortar cubes soaked in 5% sodium sulphate solution demonstrated consistently improved resistances to sulphate attack as ash content increased in the mortar. Similar results were also observed in water absorption tests. Modulus of rupture of all concrete beam...

Sustainable Pervious Concrete Incorporating Palm Oil Fuel Ash as Cement Replacement

Pervious concrete is one of the best materials used in sustainable drainage system to control the stormwater at source. The use of waste materials in concrete is able to reduce the negative impacts of concrete towards the environment. Therefore, this study presents the development of a sustainable pervious concrete by partially replacing cement with palm oil fuel ash (POFA) from palm oil industry. Properties, including void content, compressive and tensile strength as well as permeability were discussed. The results indicated that it is possible to produce sustainable pervious concrete by incorporating POFA. Furthermore, pervious concrete containing POFA showed higher water permeability and void content but lower compressive and tensile strength than control pervious concrete. However, the obtained compressive and tensile strength were within the acceptable range which is reported for strengths of pervious concrete.

Joint seals for hydraulic structures in severe climates

AbstractThis paper presents laboratory test data on 21 joint seals: 10 field-moulded sealants (FMS; 1- and 2-components polyurethanes, polysulphides, silicones, etc.) and 11 preformed seals (neoprene, silicone, high-density open-cell and low-density closed-cell foams, etc.). The aim was to evaluate their performance in submerged, partially submerged and essentially dry conditions in extremely severe climates. These seals were tested on cement mortar substrates as well as on steel substrates. The tests carried out on FMS were: adhesion-in-peel strength, compression-extension cycling at severe temperatures, Shore A hardness, weatherability and modulus of elasticity, etc. On preformed seals, the tests conducted were weatherability, % recovery and load deformation behaviour, etc. Conclusions, recommendations and the specific suitability of joint seals with cement mortar and steel substrates are reported. The general conclusion is that even though the joint seals evaluated had similar base chemical constituent...

Effect of Curing on Shrinkage and Expansion of Surface Repair Mortars

Hydro-Quebec has undertaken a major study on the evaluation of repair materials for concrete surfaces damaged by erosion. Shrinkage-expansion and compressive tests, among others, were carried out on 36 different products: 12 cementitious mortars and grouts, eight cement-based mortars containing styrene-butadiene rubber (SBR), four cement-based mortars containing acrylics, and 12 epoxy mortars. For each mix, four 25 by 25 by 275-mm bars and six 51 by 51 by 51-mm cubes were prepared for shrinkage-expansion and compressive-strength tests, respectively. Specimens were demolded after 24 h and placed at 21°C and 100% relative humidity for another 24 h. After that, half the bars were put in lime-saturated water, the other half in air at 50% relative humidity (both cured at 21°C). With respect to the cubes, half were placed in air at 21°C and 50% relative humidity, the others in a moisture chamber. Among the 35 products tested, two cementitious grouts made with special cement and artificial aggregates showed the lowest shrinkage-expansion behavior and the highest compressive strength (over 80 MPa). Two polymer-modified cement-based mortars containing SBR had shown large water expansion and air shrinkage, whereas another cement-based mortar containing SBR showed little shrinkage expansion and high compressive strength. Four of the 12 high sand: epoxy ratio mixes exhibited very large water expansion, whereas most products showed little air shrinkage.

Workability, Compressive Strength and Leachability of Coal Ash Concrete

One of the essential steps for planning solid waste management towards sustainable development is to reuse solid waste in the construction industry. Coal is one of the worlds most important sources of energy, fueling almost 40 % of electricity worldwide. Malaysia is commonly producing electricity through burning millions of tonnes of coal. This process generates around 8.5 Mt of coal ash, which comprised of 80 % Fly Ash (FA), and 20 % Bottom Ash (BA) as waste. The study aims to investigate the workability, compressive strength and leachability of concrete containing BA and FA as replacement of sand and cement. Cement was substituted with 20 % of FA by mass and fine aggregate was replaced with BA at 0, 20, 50, 75 and 100 % in the concrete mix. The results show that the percentage sum of SiO2, Al2O3 and Fe2O3 (the main chemical composition in coal ash) in FA and BA are about 78.82 % and 83.24 %. The leaching test showed that the heavy metal concentrations in leachates are much lower than recommended in the USEPA SW 846. Workability of concrete was reduced by increasing BA content as a sand replacement in the concrete mixture. After 91 d and 180 d curing periods, the compressive strength of both the experimental and control samples of concrete were roughly comparable. It can be concluded that BA and FA can be used as a replacement of sand and cement in normal concrete without any environmental problem.