After finding the properties of geopolymer mortar developed in the present study, the research was directed to develop ultrafine ground granulated blast furnace slag-based geopolymer concrete. Fresh and hardened state tests were performed on a total of 21 numbers of ultrafinely ground granulated blast furnace slag based geopolymer concrete.
Contents
List of Tables
Nomenclature
Loads Fr carried by specimen at failure in tensile Fc loads carried by specimen at failure in oblique shear tests.
Introduction
Overview
In the coming years, it is expected that the demand for concrete and therefore for cement will increase as a result of the improvement of human life. Moreover, the use of these by-products largely meets the need for recycling and reuse of waste, avoiding the problems of their disposal in the form of landfills, which leads to soil poisoning and groundwater pollution.
Geopolymer
Therefore, the use of these by-products in the preparation of concrete eradicates the disposal problem and ultimately minimizes the environmental impact caused by industrial processes. Therefore, the use of these by-products in the preparation of concrete eradicates the disposal problem and ultimately minimizes the environmental impact caused by industrial processes.
Sources of Geopolymer
- Flyash
- Silica fume
- Rice husk ash
- Metakaolin
It differs from air-cooled blast furnace slag by its relatively high porosity and low bulk density. It contains less than 10% CaO, so it is also known as low-calcium FA.
Defects in Reinforced Concrete Structural Members
Repair improves the function and performance of a structure, restores or increases its strength and rigidity, improves the appearance of the damaged concrete surface, provides waterproofing, prevents the entry of moisture, oxygen, chloride, carbon dioxide, etc. Some of the situations in which retrofitting is adopted include improving the capacity of the structure to withstand underestimated loads and design flaws, to eliminate premature failure due to insufficient detailing, seismic retrofitting to meet standard requirements /codal, restoring the load-bearing capacity of structures affected by corrosion or cracks, etc.
Historical Background
- Geopolymer and geopolymeric systems
- Repairing and strengthening of reinforced concrete members
On the contrary, the compressive strength was found to increase due to the addition of OPC to the geopolymer concrete. Due to the addition of CFW to the geopolymer, the porosity of the system increased.
Scope of the Present Study
The crack development and crack modes in the retrofitted beams were independent of the thickness of the GUSMRC strips. There are many materials and technologies readily available for use in concrete repair and curing. Some repair and curing materials are: epoxy resin, fiber reinforced polymer, steel plates, etc.
However, these repair and strengthening materials are expensive materials and the techniques involved in repairing and strengthening using these materials are advanced and therefore require skilled labor for the job. Geopolymer, which is a by-product and has the potential to be used as a repair and reinforcement material, can be used as a replacement for these expensive materials and advanced technologies. The preparation of geopolymer mortar and concrete is similar to that of Portland cement mortar and concrete and can be prepared easily.
Objectives of the Thesis
Organization of the Thesis
Appendix has been added to provide detailed calculation of mix design and prediction of load bearing capacity of test beams.
Closure
Material Characterization
- Overview
- Portland cement
- Ultra-fine ground granulated blast furnace slag
- Flyash
- Aggregates
- Admixture
- Steel reinforcement bars
- Mix Design
- Design of Reinforced Concrete Beam
- Closure
In addition, the compressive strength of the cement was also evaluated as per the provisions of IS 4031 (Part. The values of various properties of the PC were found to be within the range mentioned in the relevant Indian Standards of Practice. Numerous types of alkali activators were used in geopolymer mixtures by researchers to start the geopolymerization process.
The amount of NaOH pellets (solids) in a solution varied depending on the concentration of the solution. The typical load capacities of the beam, evaluated by theoretical and experimental methods, are shown in Table 2.11. Mix designs were carried out to determine the mixture proportion of concrete for casting the RC beams.
Development and Testing of Geopolymer Mortar
Introduction
Early strength development was observed in geopolymer mortar by various researchers such as Brough and Atkinson [22], Oner et al. Pozzolanic activity increases due to increase in binder fineness, which contributes to early formation of reaction products and thus leads to early strength [104]. However, such mortar or concrete exhibits lower setting time and workability compared to the mortar or concrete made with the same binder of lower fineness [20].
A larger available particle surface area of the binder facilitates the increased pozzolanic activity for the immediate formation of reaction products. These reasons are due to the lower setting time and the loss of workability of mortar and concrete mixtures. Flyash (FA) and superplasticizer (SP) were added to the GPM to change the properties and achieve satisfactory setting time and workability while maintaining the property of early strength gain.
Experimental Investigation
- Materials
- Mix proportions
- Specimen preparation and curing
- Experiments
- Setting time
- Workability
- Compressive strength
- Microstructure study of geopolymer mixes
- Statistical analysis of test data
Mixtures with NaOH as alkali activator showed similar setting times for a/b ranging from 0.55 to 0.65. The difference in the setting times from the mixtures with other types of mixture is, however, nominal. Mixes with SN-based SP exhibited lower FI compared to PE-based SP unless added to the mix by direct addition in the alkali activator.
The use of NaOH as an alkaline activator in the mixtures contributed to a better strength development compared to mixtures with Na2SiO3 and NaOH together as an alkaline activator. Although the addition of FA in the mixes slowed down the setting time and improved the workability as shown in the figure. The reduction in early strength gain was more significant in mixtures with FA 40 and 50 content.
Closure
Strength enhancement properties exhibited by mixtures with PE-based SP are found to be better than SN-based. SP dosage higher than 1.5% of the total binder content leads to low strength of the mixtures. Alkali concentration has a significant role in regulating the setting time, workability and strength gain of the mixtures.
Low (8 M) and high (14 M) concentration of NaOH solution results in a similar pattern of reduced strength gain in the mixtures. The maximum rate of strength gain and strength at all ages has been observed in mixtures with a NaOH concentration of 10 M. Variations in the time of addition of SP to the mixtures appear to be responsible for the variations in setting time, workability and rate of strength gain .
Development and Testing of Geopolymer Concrete
Introduction
- Materials
- Specimen preparation and curing
- Experiments
To activate the geopolymerization process, sodium hydroxide (NaOH) solution was used as an alkaline activator. Subsection 2.2.1 Portland cement of Chapter 2 presents details of OPC properties. SP types SN and PE were added to GPC in one of the following three types:-.
The curing of the samples was carried out in a similar manner to the GPC samples. Before placing the concrete in the pull-out test specimen, the rebar was placed in the mold and stood vertically with the help of a special device. To compact the concrete, the molds were vibrated after pouring the concrete in each layer.
Pull-out test specimen
Bond strength of GPC and PCC mixtures was evaluated based on bond strength with reinforcement (BSr) and with 2, 6 and 12 months old PCC substrate (BSc). The inclined shear test according to ASTM C882/882M-13a [124] was performed on the GPC and PCC mixtures at 3 and 28 days to determine the bond strength with PCC substrate.
Rebar
Pulling force
Experimental Observations .1. Workability
- Bond strength (slant shear)
While for others, especially when large amounts of SP were added, the strength of the GPC-rebar joint decreased due to the increase in the slump value. In the case of G1 GPC mixtures, a slight increase in the strength of the GPC-rebar joint was observed due to the higher compressive strength value. It was found that the bond strength of GPC with PCC gradually decreases with the aging of PCC {Fig.
The observation was the same for both early (3 days) and later (28 days) aged bond strength of the samples. The bond strength of blends decreased monotonically as the amount of SN-based SP in the blends increased. The trend lines for various UGGBS-based GPC blend groups show that increase in compressive strength increases the bond strength of GPC with PCC.
Closure
Addition of fly ash (FA) to the UGGBS-based GPC contributes to monotonous improvement in workability. In the case of bond strength results, the addition of FA improves the performance of the mixes, but up to a low FA content level. The compressive and bond strength of the blends improve to lower level of PE-based SP dosage.
In the case of mixtures with SN-based SP, the addition of SP results in a monotonic decrease in compressive and bond strength. The SP addition time shows a significant influence on the fresh and solid state properties of UGGBS-based GPC. Other types of SP additives are not useful in improving the properties of mixtures.
Repairing of RC Beams using Geopolymer Mortar
Introduction
- Materials
- Method of beam preparation and repairing with mortar
The repair of the cracks was carried out with Portland cement paste (PCP) and Portland cement mortar (PCM); and geopolymer paste (GPP) and geopolymer mortar (GPM). Laboratory tests were conducted to evaluate the PCP's fresh and cured state properties. The choice of GM20 as repair agent was based on fresh and cured properties of the GPM mixtures.
The fresh and hardened properties of the GPM mixture GM20 are shown in Table 5.5. After completion of the curing period, the RC beams were removed from the wet cloths and allowed to surface dry. However, for repaired beams, the load was applied until the beams failed.
Experimental observations
- Fully damaged RC beams
The ductility ratio (DR) was found to be 2.89, which was lower than that of controlled beam, B1. The first crack in the repaired RC beam occurred very early at 4.01 kN followed by subsequent cracks, while the first crack in the checked beam occurred at 19.44 kN. The occurrence of first crack at a very early stage is attributed to the fact that PCM achieves very low compressive and bond strength at early ages.
This observation is supported by the observation that the cracks in the PCM repaired B1R beam appeared at the same location as the cracks in the control beam. 5.15 (a) and (b) that the PCM placed in the crack during the repair was released from crack no. When carefully observing the cracks (Fig. 5.16), it was found that the cracking occurred because the PCM separated from the old concrete surface of the cracks mainly due to the breakdown of the bond between the PCM and the older concrete of the beam.
