Performance-based RCPT specification for geopolymer concrete: Modified voltage protocol and chloride resistance classification

Concrete modified with various chemical and mineral admixtures are gaining popularity as construction materials, but inclusion of admixtures raises questions about the validity of standard tests of transport properties and conductivity. To explore most representative tests, the present study has evaluated and compared transport properties by several methods: standard rapid chloride permeability test (RCPT), modified RCPT, electrical conductivity, electrochemical impedance spectroscopy (EIS), and salt-ponding tests. Three normal concretes and nine high-performance concretes including different combinations of mineral admixtures were investigated. Results show that the effects of heat generation in RCPT cells were dependent on the types and combinations of mineral admixtures, and that pore solutions had definite effects in RCPT results. The relatively expensive and difficult test of EIS can be replaced by one-minute RCPT and conductivity meter test. The correlations between salt-ponding tests and various RCPTs were found to be weak due to different mechanisms involved.

Effect of mixing proportions of concrete on its electrical conductivity and the rapid chloride permeability test (ASTM C1202 or ASSHTO T277) results

The construction industry plays a vital role in the economic development and overall progress of any country. Construction activities have significant impact on the economy, but their environmental consequences cannot be overlooked. The excessive use of construction materials particularly cement and steel, which are among the most commonly used construction materials, has become a major environmental concern, as these materials are also key sources of carbon emissions. Moreover, the raw materials required for the preparation of cement and Steel are also depleting at a rapid pace. Therefore, it is necessary to conduct research studies to find new alternative materials which can reduce the consumption of cement and steel in the concrete. Fly ash can be used as binding agent in concrete as it has good cementation properties and is abundantly available. To enhance the mechanical performance of geopolymer concrete (GPC), polypropylene fibers (PPFs) were incorporated in varying ratios (0.5% to 1.5% by volume). The samples were prepared to test the mechanical and durability properties of the concrete. Compressive Strength, Flexural Strength, and Split Tensile Strength test was carried out to conclude the mechanical properties of the geopolymer concrete against different percentages of polypropylene Fiber. Acid attack and rapid chloride permeability tests were conducted out to evaluate the durability of the concrete. The research findings depicted that the greatest compressive strength and split tensile strength are obtained at 1% PPFs GPC. The least amount of chloride penetration was demonstrated by GPC, at 1.5% PPFs.

Production of geopolymer concrete using natural pozzolan: A parametric study

Ferrochrome slag (FS) and ground granulated blast furnace slag (GGBFS) were used as resource material in geopolymer concrete mixtures. A mixture of 10 M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used as the activator. After the two different slag‐based geopolymer concrete (SGC) mixtures were prepared and molded. They were kept at 80°C for 24 hr, and then the SGC samples were cured in 23 ± 1°C water for 27 days. Samples that completed the curing times were exposed to the 300 freeze–thaw (F–T) cycles. The compressive strength, ultrasonic pulse velocity, relative dynamic elasticity modulus values, weight changes, and appearances of the SGC samples were examined at the end of every 50 F–T cycles. Scanning electron microscopy analysis was performed to examine the microstructure changes of the samples after 300 F–T cycles. As the GGBFS proportion in the SGC mix increased, the mechanical properties of the samples against the F–T effect increased. Samples containing 100% FS and 75% FS fell apart at the end of 150 and 200 F–T cycles, respectively. The deterioration of the geopolymer gel structures of the samples exposed to F–T was decreased with increasing GGBFS ratio in the mix.

This research discusses the compressive strength of geopolymers made from coffee grounds as an additional material in geo-polymer fly-ash based concrete. The research aims to design a geopolymer concrete mix based on coffee grounds and fly ash, determine the compressive strength of geopolymer concrete based on coffee grounds and fly ash, and identify the optimal percentage of coffee grounds in geopolymer concrete production. The study has limitations, such as a concrete strength of 35 MPa, testing at 7, 14, and 28 days, and the use of an alkali activator with a molarity of 8. The research method employed involved experiments conducted in the material and concrete laboratory with the variable percentage of coffee grounds ranging from 0% to 20%. The use of coffee powder in the geopolymer concrete mixture as a replacement for fly ash has an impact on reducing the slump value by up to 18.52 % and reducing the specific gravity of the concrete by up to 6.55%. However, the use of up to 10% coffee powder still produces compressive strength values above the minimum requirement for structural concrete compressive strength, namely 20 MPa. Thus, a mixture with 10% coffee grounds can still be used as an alternative construction material that is more economical and sustainable.

The effects of surface treatments on rapid chloride permeability tests

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.

The present study aimed at assessing mechanical and durability characteristics of ground granulated blast furnace slag (GGBS)-based geopolymer composites at 5%, 10%, 15%, 20%, 25%, and 30% replacement proportion of silica fume at 12 molarity of NaOH. Mechanical properties were assessed using compression and tension tests, whereas durability characteristics were evaluated using ultrasonic pulse velocity test (UPV), acid test, and rapid chloride permeability test (RCPT), and water absorption (WA) test. Additionally, reduction in mass and strength were also determined due to the acid action on the developed composites. A correlation of compressive strength was also established with the splitting tensile strength, UPV, RCPT, and WA. The presence of silica fume and high NaOH concentration in GPC tends to improve the mechanical strength up toa certain level. UPV values obtained were falling in the range of medium to good category. Chloride ion penetration and water absorption values were reduced by around 23% and 26%, respectively, at 10% silica fume replacement. Mass loss and strength loss were reduced as the % of silica fume increased. A good correlation of compressive strength was obtained with tensile strength, UPV, and RCPT with a coefficient of determination of 0.9681, 0.9665, and 0.9208, respectively. Poor correlation was obtained between compressive strength and water absorption.

Modelling chloride penetration resistance of Supplementary Cementitious Concrete and compressive strength with pulse velocity

Rapid urbanization and modern construction approach create an impervious island in urban and semi-urban areas, which leads to make a situation of artificial flooding. The major reason for making impervious islands is due to the use of cement-based concrete pavement in and around the urban areas. As a result, stormwater runoff is promptly collected and discharged to various receiving main drains, rivers, and, eventually, the sea. This leads to decrease infiltration and depletes the water table. To overcome these problems, pervious concrete is very essential to be laid down in the parking areas, low volume road pavement, sidewalks, driveways, tennis courts etc. in place of normal cement concrete. Normal porous concrete is a special type of cement concrete with high porosity, allowing water to percolate into the sub-grade. But cement is said to be the most unsustainable material requiring huge energy, emitting huge carbon dioxide and consuming huge natural resources during its production. On the other hand, alkali-activated alumina-silica rich waste material made geo-polymer concrete is said to be a sustainable alternative to cement concrete. This paper reports on the preparation and properties of an eco-friendly geo-polymer self-compacting pervious concrete mix using fly ash under the sun curing. Various laboratory tests like compressive strength, flexural strength and permeability of prepared geo-polymer concrete were taken up. The laboratory results of sun-cured geo-polymer concrete were compared to water-cured normal concrete and found more or less nearer to each other. To establish the structural performance of prepared geo-polymer pervious concrete, a pilot study was taken up using the prepared material as shoulder material. Rebound hammer tests were conducted at the field and compared to laboratory results and found consistent. The compressive strength obtained was found more than 15 MPa for which it can be used also used for applications with low traffic volume. The location of the pilot project: Lat 20°21'10.58"N, Long: 85°54'54.78"E village-Aradiapada, Cuttack Odisha India.

Incorporating crumb rubber in slag-based geopolymer: Experimental work and predictive modelling

Environmental impact assessment of fly ash and silica fume based geopolymer concrete

The growing demand for environmentally friendly construction has been the driving force behind the production of sustainable and cost-effective construction materials. Portland cement (PC), which is not considered an environmentally friendly material, is an important ingredient in concrete. In contrast to Portland cement, geopolymers are gaining increased interest as low-CO2 emission binders. This research consists of two basic stages, the first stage investigates the effects of many parameters on the properties of geopolymer concrete based on fly ash, in particular the compressive strength, tensile strength, and flexural strength .The parameters included were fly ash content, degree of solution molarity, alkaline liquid ratio to fly ash content, curing conditions, fine aggregate to coarse aggregate ratio. Second stage of the research concerned with the durability of geo-polymer concrete developed using fly ash class-F. As a guide for assessing the durability of geo-polymer concrete, the efficiency of ordinary Portland cement (OPC) concrete is also discussed. The influence of salt solutions of different concentrations through various periods of wetting – drying cycles on the weight loss, water absorption, and geo-polymer concrete has been investigated for its compressive strength. According to the first stage results, the best parameters which gave the highest geo-polymer concrete's mechanical properties, were: fly ash content of 400 kg/m3, 16 M degree of molarity, curing time of 3 days in oven, the ratio of alkaline liquid to the content of fly ash equals 0.5 and ratio of fine aggregate to coarse aggregate equals to 1:2, where the compressive strength reached its highest value (387 Kg/cm2). The results of second stage revealed that geopolymer concrete is less affected than cement concrete with respect to compressive strength and more affected in weight loss and water absorption. Geopolymer concrete showed an increase in water absorption compared to OPC concrete, after 9 weeks of wetting – drying cycles in salt solutions, by about 176% &184% for 5% & 10% solutions concentration, respectively. Also, more weight loss for geopolymer concrete specimens was revealed compared to OPC concrete by about 33% & 30% for 5% & 10% solutions concentration, respectively. However, the geopolymer concrete (GPC) showed less reduction in compressive strength due to the exposure to salt solutions (wet – dry cycles) than OPC. For both solution concentrations (5% & 10%), the average reductions in GPC compressive strength were 18%& 25%, respectively, while the corresponding reductions in OPC were 25% & 34%.

A comprehensive mechanical and physico-chemical characterization of fly ash-based geopolymers