Effect of Silpozz and Fly Ash on Strength and Durability Properties of Concrete in Sea Water

This paper presents the results of an experimental investigation carried out on strength and durability properties of plain and blended cement concrete exposed to sea water. The mix design is targeted for M30 grade concrete. The plain cement concrete samples made 0 % replacement of fly ash (FA) with cement and the blended concrete samples made 10, 20, 30, 40 and 50 % replacement of FA with cement. Another blended cement concrete samples also made with 10 % replacement of FA and 10, 20, 30, and 40 % replacement of silpozz (silica fume) (SF) with cement. Two set of samples (cube) have been prepared. One set of sample, after 28 days of normal water curing (NWC) was being immersed in sea water for 7, 28 and 90 days and the other set of samples have been cured in normal water for 7, 28 and 90 days and their compressive strength measured. The investigation reflects that the percentage increase in compressive strength for blended cement concrete in NWC is better than the samples in sea water curing (SWC) after 28 days of NWC. The water soluble chloride and acid soluble chloride were found less for blended cement concretes up to 10 % replacement of FA and 30 % replacement of SF with cement.

This paper reports on the result of an experimental investigation carried out to study the compressive strength and sorptivity properties of blended cement concrete exposed to 5% and 10% MgSO4 solution using fly ash (FA) and silpozz. Usually in sulphate environment the minimum grade of concrete is M30 and the mix design is done for target mean strength of 39 MPa. Silpozz is manufactured by burning of agro-waste rice husk in designed furnace in between 600o to 700oC which is one of the main agricultural residues obtained from the outer covering of rice grains during the milling process. There are four mix series taken with control mix. The control mix made 0% replacement of FA and silpozz with Ordinary Portland Cement (OPC). The first mix series made 0% FA and 10-30% replacement of silpozz with OPC. The second mix series made with 10% FA and 10-40% replacement of silpozz with OPC. The third mix series made 20% FA and 10-30% replacement of silpozz with OPC and the fourth mix series made 30% FA and 10-20% silpozz replaced with OPC. The samples (cubes) are prepared and cured in normal water and 5% and 10% MgSO4 solution for 7, 28 and 90 days. The studied parameters are compressive strength and strength deterioration factor (SDF) for 7, 28 and 90 days. The water absorption and sorptivity tests have been done after 28 days of normal water and magnesium sulphate solution curing. The investigation reflects that the blended cement concrete incorporating FA and silpozz showing better resistance against MgSO4 solution when compared to normal water curing (NWC) samples.

This study examines the effect of seven different curing regimes (normal water, marine environment, ambient, jute bag, polythene bag, accelerated water, and carbonation curing) on the mechanical properties and durability of concrete that incorporates marble dust as partial replacement of cement at 0%, 2.5%, 5%, 7.5%, 10%, 12.5%, and 15% replacement rates. The curing regime considerably impacted minimizing the compressive, flexural, and split tensile strength losses induced by increased marble dust content. Under normal water curing, an optimum 7.5% marble dust dosage resulted in a 9.5% increase in 28-day compressive strength over the control mix. Carbonation curing resulted in higher 28-day flexural strengths (up to 12.5% marble dust) than normal water curing. Marine environment curing reduced strength significantly (up to a 30.1% decrease at 7-day compressive strength at 15% marble dust) due to chloride ion interference. Water absorption dropped by up to 15.7% at the optimal 7.5% marble dust dosage under normal water curing but increased by up to 3.9% under ambient curing, highlighting the importance of adequate curing for pozzolanic reactions. Rapid chloride permeability testing revealed up to 53.9% lower charge passing values under normal water curing at 15% marble dust, demonstrating better chloride resistance when compared to other curing regimes. Continuous hydration and pozzolanic reaction facilitation through appropriate curing procedures, such as conventional and accelerated water curing, significantly increased performance at optimal marble dust dosages. The study emphasizes the importance of adjusting curing regimens to optimize the use of marble dust as a sustainable SCM in concrete production.

This article reports the mechanical properties of blended concrete containing fly ash (FA) and silpozz exposed to seawater. The reduction in strength is evaluated between normal water curing (NWC) and seawater curing (SWC) samples by strength reduction factor (SRF) in percentage. The microstructural analysis is done by scanning electron microscopy (SEM). It is revealed from the test results that the SRF for compressive strength is 4% for 10% FA and 20% silpozz replaced with ordinary Portland cement (OPC) for 6 months exposure to seawater. The SRF for flexural strength and split tensile strength is 1 and 0.80% at 90 days exposure. The minimum slip is 1 mm after 28 days of testing bond strength for NWC samples. The SRF in bond strength is also evaluated and found as 10.35% for 28 days SWC samples. The dense and compact microstructure was observed in 28 days NWC samples.

The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.

This article presents the strength and sorptivity of concrete using fly ash (FA) and silpozz exposed to seawater. Conventional concrete made with 100% cement. First blended concrete series made with 0% FA and 10–30% silpozz replaced with cement and second series made 10% FA and 10–30% silpozz. The studied parameters are compressive strength for 7, 28, 90, 180 and 365 days and flexural strength and split tensile strength for 7, 28 and 90 days of seawater curing (SWC) and normal water curing (NWC) samples. Modulus of elasticity and strength reduction factor (SRF) in bond strength along with slip of 28 days SWC samples are also studied. Water absorption and sorptivity were observed as durability indicator. It reveals from the present investigation that incorporation of silpozz helps to improve the strength and reduces sorptivity of concrete against seawater.

Experimental investigations on the early age, strength gain properties of fly ash blended cement concretes containing low and high volume fly ash replacement were studied. Concrete mixes were prepared with two different fly ash contents and varying concrete ingredients with water to binder ratio (w/b), fine to coarse aggregate ratio (F/c) and accelerator dosage. Five different curing techniques, namely controlled humidity curing; hot air oven curing, steam curing, hot water curing and normal water curing were adopted for curing the fly ash based concretes. Test results showed evidence the influence of accelerating admixtures and accelerated curing for obtaining the high early strength properties in fly ash mixed concrete. Most notably a maximum 1 day compressive strength of 40.20 MPa and 34.60 MPa with low (25%) and high (50%) volume fly ash concretes were obtained respectively in this study. Experimental results clearly indicated that the improvements on the strength gain properties with the careful selection of mix ingredients; accelerator addition and accelerated curing in fly ash based concrete mixes. Also, significant improvements on the flexural strength, elastic modulus, dynamic modulus and the ultrasonic pulse velocity test were noticed.

Concrete is one of the most used manufactured materials in the world. Fly ash (FA) is a byproduct produced from pulverized coal combustion in power generation. A total of 0.08 million tons of class F fly ash is produced from a coal-based power plant yearly in Barapukuria, Bangladesh, whose disposal is of a great issue. Therefore, this study aims to explore the possibility of using class F FA in concrete construction as a supplementary cementitious material. In this study, two different water-to-cement ratios (0.4 and 0.5), each with five cement replacement levels numerically, 0%, 10%, 20%, 30%, and 40% with FA are used. Various tests are performed on cylinder and beam specimens to assess physical, mechanical, and durability properties, such as workability, density, compressive strength (CS), splitting tensile strength (STS), flexural strength (FS), chloride ion penetrability (CIP), and shrinkage. Analyzing the results, it is reported that workability increases and density decreases with the increasing FA replacement. Mechanical properties mostly decrease with increasing FA content. However, the strength gained with age is higher for concrete with FA compared to the control concrete. The CIP reduces with FA replacement, especially at 56 days of age. Shrinkage value reduces 82% at 40% replacement FA replacement and w/c ratio 0.4. However, at 10% FA replacement and concrete age of 56 days, mechanical strength loss is infinitesimal or even better compared to the control concrete. Thus, a low replacement percentage of FA with a high curing period is a suitable concrete cement alternative.

Effect and limitation of free lime content in cement-fly ash mixtures

Coupled effect of poly vinyl alcohol and fly ash on mechanical characteristics of concrete

Pakistan being one of the most urbanized countries of the region having a large number of industries which have been known to produce large quantities of byproducts and wastes. For economic and environmental aspect the industrial waste reuse is appreciable because environmental contamination is the major issue associated with rapid increase in the byproduct and waste generated in the forms of fly ash and marble dust waste due to industrial activities. This study examines the mechanical properties of fresh and hardened cement mortar by using fly ash as partial replacement of cement and waste marble dust as partial replacement for fine aggregate in cement mortar at various percentages (0%, 5%, 10%, 15% and 20% by weight of the cement and fine aggregate) with water. An experimental investigation for the measurement of consistency, initial setting time and final setting time of cement with fly ash replacement were determined by using the Vicat apparatus. Consistency of cement mortar (Workability) with fly ash and waste marble dust replacement was determined by using flow table test. Cubes of the samples with fly ash and waste marble dust replacement as cement and fine aggregate were used to determine the compressive strength of hardened cement mortar. The test results showed that addition of fly ash and waste marble dust into cement mortar mixture significantly increased its compressive strength, initial setting time, final setting time and consistency of cement mortar, while consistency of cement was decreased as compared to conventional cement mortar. This study ensures that reusing of fly ash and waste marble dust as substitutes in cement mortar gives a good approach to solve industrial waste disposal problems.

Pakistan being one of the most urbanized countries of the region having a large number of industries which have been known to produce large quantities of byproducts and wastes. For economic and environmental aspect the industrial waste reuse is appreciable because environmental contamination is the major issue associated with rapid increase in the byproduct and waste generated in the forms of fly ash and marble dust waste due to industrial activities. This study examines the mechanical properties of fresh and hardened cement mortar by using fly ash as partial replacement of cement and waste marble dust as partial replacement for fine aggregate in cement mortar at various percentages (0%, 5%, 10%, 15% and 20% by weight of the cement and fine aggregate) with water. An experimental investigation for the measurement of consistency, initial setting time and final setting time of cement with fly ash replacement were determined by using the Vicat apparatus. Consistency of cement mortar (Workability) with fly ash and waste marble dust replacement was determined by using flow table test. Cubes of the samples with fly ash and waste marble dust replacement as cement and fine aggregate were used to determine the compressive strength of hardened cement mortar. The test results showed that addition of fly ash and waste marble dust into cement mortar mixture significantly increased its compressive strength, initial setting time, final setting time and consistency of cement mortar, while consistency of cement was decreased as compared to conventional cement mortar. This study ensures that reusing of fly ash and waste marble dust as substitutes in cement mortar gives a good approach to solve industrial waste disposal problems.

This study evaluates the effect of particle size distribution (PSD) of high calcium fly ash on high volume fly ash (HVFA) mortar characteristics. Four PSD variations of high calcium fly ash used were: unclassified fly ash and fly ash passing sieve No. 200, No. 325 and No. 400, respectively. The fly ash replacement ratio of the cementitious material ranged between 50-70%. The results show that with smaller fly ash particles size and higher levels of fly ash replacement, the workability of the mixture was increased with longer setting time. There was an increase in mortar compressive strength with finer fly ash particle size, compared to those with unclassified ones, with the highest strength was found at those with fly ash passing mesh No. 325. The increase was found due to better compactability of the mixture. Higher fly ash replacement reduced the mortar’s compressive strength, however, the rate was reduced when finer fly ash particles was used.

Since cement manufacturing causes 7– 8% of total global CO 2 emissions, attempts have been made to minimize cement consumption. One method is to introduce pozzolans, commonly fly ash (FA), as supplementary materials to Ordinary Portland Cement (OPC). The main drawback of incorporating FA into cement is the reduction of early strength in concrete. This can be countered by incorporating Nano silica (NS) into the FA - OPC mix. Workability, compressive strength (3, 7, 28 & 100 day), sorptivity and thermogravimetric analysis (TGA) testing was carried out on cement paste specimens with FA replacements from 0% to 70% and NS percentages from 0 to 6%. All mixes were prepared with a 0.4 water binder ratio and a superplasticizer dosage to achieve equal workability for all mixes. Results showed that workability reduces with the increase of NS. Also, for a given %NS, compressive strength reduces with the increase of FA for early age strength, while 30% FA replacement gives optimum strength at 100 days. A 3% NS content for constant %FA gives optimum strength beyond 28 days. Sorptivity too is lowest at 30% FA replacement with 3% NS. Therefore 30% FA replacement with 3% NS gives optimum performance for both strength and durability. The mix with 50% FA replacement and 3% NS (a genuinely HVFA mix) is promising as a practically useful mix. The TGA enables us to obtain the Calcium Hydroxide (CH) consumed for pozzolanic reactions; this is used to validate a model that explains the strength variations in these mixes.

Too much CO2 is released during cement production. In many researches, the use of natural or recycled compounds plays an important role in the cement composition. The use of these components contributes both to reducing the amount of waste and to protecting the environment in nature. It is possible to produce an environmentally friendly concrete, thanks to its being a fly ash thermal power plant waste and its use as mineral additive in terms of its composition. In this study, it is aimed to produce impermeable concretes with the use of C type fly ash as substitutes for cement in concrete composition in substitution rates of 10 %, 30 % and 50 %. In order to reduce the permeability of concrete in this direction, as a result of grinding the fly ash in the ball mill for 0, 10, 20, 30, 45 and 60 minutes, concrete samples were prepared with and without admixture (Reference). Capillarity test was performed to determine the permeability at the end of cure periods of 28 and 90 days on concrete samples. According to the results obtained at the end of 28 days, the best impermeability was achieved in the mixture with 50 % fly ash replacement and 60 minutes grinding time. In 90 days, the best impermeability was obtained in the mixture with 30 % fly ash replacement and 0 minutes of grinding time. As a result, it was seen that permeability decreased with increasing thinness and substitution rate of fly ash in concrete composition.