Performance evaluation of HVFA content in cement concrete incorporating filler additives: rheology and mechanical properties

For a better sustainable progressive world, construction industry turned wider gradually. It is well known fact that cement concrete is main component of construction for our modern civilization. Now days, fly ash is used as the most potential replacement material in cement concrete, as production of cement very badly harm our environment. Reports show that one tonne cement produces one tonne carbon dioxide in our environment and responsible for global warming. After successive research work, it is proven that replacement of high volume fly ash (above 50%) which is pozzolanic in material (consists of siliceous and aluminous compounds) in cement paste helps to achieve high strength, porosity, heat of hydration, micro structure as well as very economical and eco-friendly against normal cement paste. This paper mainly highlights on the detailed study of rheological and strength properties of high volume fly ash concrete (50%-70% replacement of cement in various grades of fly ash mixed as per IS standards) in addition with various additives and melamine based admixture. In addition to this, other properties such as consistency, hardening and stiffening, workability, mechanical properties are studied. This overall study include experimental program on various concrete specimen with varied cementitious content along with admixtures.


Introduction
At late 1980s High volume fly ash concrete invented by the Canadian Centre for Mineral and Energy Technology (CANMET) for structural uses [1].In accordance with American Society for Testing & Materials (ASTM) C618, fly ash defined as Class F fly ash and Class C fly ash.These two types of fly ash are categorized by their amount of chemical (i.e.calcium, silica, alumina and iron) content in the ash.Fly ash mainly found in powder form having granulometry of 0.5 -100 µm, mainly used as supplementary cementitious material (SCM) for Portland cement [2].Thorough experimental work shows use of fly ash in concrete is highly advantageous such as it instigates improved mechanical, physical as well as rheological properties.Hence, the main focus for utilization of fly ash in concrete is to achieve satisfactory values of compressive strength at lower cement content.It is also observed that application of mineral admixtures and super plasticizer in fly ash concrete imparts beneficial effects to concrete, accelerate the high strength, workability, setting time, sulphate resistance [5].
This comprehensive literature study emphasizes on collected data on fly ash based concrete mixes including additives.The materials incorporated in various previous experimental works include nanosilica, condensed silica, improved HVFA properties up to 70% replacement.The overall review will assist to choose suitable combination of HVFA concrete with other mineral and chemical admixtures.This scrutiny will also help to develop HVFAC and their individual and combined effect of various additives, proper mix proportioning methodology and guidelines, helpful for construction industry in future.In this elaborate study, the main aim lies on detailed study on high volume fly ash.In concrete the percentage of replacement range from 20%-referred as low volume fly ash and above 40% as high volume fly ash [9].This current analysis is based on a comprehensive study on changes of mixture after replacement of fly ash in concrete.Observations also analyse the behaviour of concrete after applying super plasticizer and different additives with fly ash and hydraulic binder at early age and later age.

History of Work
L.Lam et.al., (1998) showed high volume fly ash can be utilized in concrete with varied watercementitious ratio, slump value, etc.Earlier experimental investigations emphasize improved strength parameters (42.5 MPa at 3-days curing stage and 85 MPa at 28-days curing stage) for replacement of 50%-70% (b/w) cement with fly ash in presence of various super plasticizers.Slump value changes with time [3].It is also observed fly ash content below 30% (b/w) is unsuccessful in meeting expected levels of performance compared to 40%, 45% and 50% fly ash content with improved results in strength (after 28 days for R.C.C. constructions) and also shows great performances in high resistivity against abrasion and on chemical attack(i.e., chloride, sulphate and acid attacks) [4,17].

Lam L. et.al., (2000)
presented with increasing amount of fly ash (high volume) in cement helps to increase porosity of paste level and also comes up with increased level of pore surface fractal dimension.In other hand it's mainly contribute during the process of heat of hydration [4].But 45%-55% fly ash in paste unreacted in degree cement hydration reaction at higher curing age [10].Research studies by Cengiz D A et al (2003) focussed on implementation of partial replacement of fine aggregates with fly ash.Utilization of fly ash as replacement of fine aggregate was studied [5,18,19].Works of M.J. Mc Carthy , R.K. Dhir (2005) shows fly ash possess huge effect on environment and as well as takes a good lead in technical and economic benefits.High volume fly ash in high range can be used as combination with Portland cement for rapid hardening.Fly ash possesses a huge aspect on environment and as well as take a good lead in technical and economic benefits.High volume fly ash in high range can be used as combination with Portland cement for rapid hardening [6].
The study also indicates addition of silica fume (5%) in high volume fly ash concrete shows very impressive result in cylinder compressive strength and tensile splitting strength but not in cube.15%-25% fly ash (b/w of cement) provides better effect on tensile strength but 45%55% fly ash replacement with cement display high larger fracture displacement and shows low load bearing capacity [9].

Jian -Hua Wu et.al., (2006)
served high volume fly ash can be utilized in concrete with varied water cementitious ratio, slump value, etc.Earlier experimental investigations emphasized to improve strength parameters (42.5 MPa at 3-days curing stage and 85 MPa at 28-days curing stage) for replacement of 50%-70% (b/w) cement with fly ash in presence of various super plasticizers.Slump value changes with time [9].It is also found out adding lime stone and gypsum with fly ash play role as a soil stabilizer which is better for environmentally friendly [10][11][12].
In addition to these studies, various authors such as S. Mukherjee et.al., (2013) conducted researches up to 60% replacement of fly ash in concrete create zero slump concrete that ' s shows high compressive strength [11] IOP Publishing doi:10.1088/1757-899X/1282/1/0120043

2.3.
Objective: Fly ash in green concrete has a immense aspect in sustainable development and step by step its research work growing that some work can be beneficial path in future i.e. from previous research studies, it is well known high volume fly ash content in cement concrete leads to enhanced mechanical strength properties on if extra additive such as silica fume (5%-10%) is added along with 1%-5% chemical admixture is added.This present experimental investigation not only highlights the utilization of high volume fly ash in high performance concrete at various cement replacement levels (CRL) but also focuses on development of a new, rational, scientific and cost-effective mix design approach.This paper mainly deals with the strength and rheological effects due to various water/binder ratios of 0.25, 0.30, 0.33 and 0.40 with various dosage of chemical activators and mineral additives.

Objective
The class F fly ash required for the experimental purpose is obtained from Gujarat, India possesses fineness modulus (F.M.) 2.06.The fly ash obtained stored in controlled conditions.Chemical tests conducted to determine the chemical properties of FA and the oxide composition of fly ash and cement is as follows: SiO 2 -22%, Al 2 O 3 -28.34%,Fe 2 O 3 -12.5%,TiO 2 -1.51%,CaO-1.79%,MgO-0.84%,SO 3 -2.25%,Na 2 O-0.42% and Loss of ingnition-2.42%.The test results for various chemical composition is given in figure 1 and figure 2.

Table: 3.1 Chemical Test Results
River sand of zone III used with fineness modulus 2.13(zone III) and specific gravity 2.55 and 20 mm nominal size coarse aggregate used, which fineness modulus 2.63 and specific gravity is 2.96.Commercial superplasticizer Sika® plastocrete® plus with composition of modified lignosulphonate is used as chemical admixture in concrete mix at 0.5 % to 5% b/w of total cementitious materials present.
Along with this in some tests, polycarboxylate ether (PCE) is also used.The specific gravity of the activator is 1.04.In some experimental series, silica fume is also used.The initial and final setting times of cement calculated in the laboratory and the values determined obtained as 150 minutes and 225 minutes respectively.Fine aggregate (F.A.) considered for this work-locally available(Zone-III) natural river bed sand.The coarse aggregates and fine aggregates utilized for concrete preparation kept oven dried maintaining S.S.D (Saturated Surface Dry) condition throughout.For designing mix proportions of various concrete mixes, following data is utilized as: nominal maximum size of aggregates adopted as 20 mm and degree of workability = 0.90 (C.F.).The target slump maintained at 100 to 120 mm.The degree of quality control maintained as good and type of exposure= mild.In this test program, normal cement binder (OPC 43 grade) used with specific gravity of cement= 3.15.The fine aggregates possess specific gravity of 2.55 and specific gravity of coarse aggregates (crushed angular) taken as 2.64.The water absorption adopted for coarse aggregates as 0.5 % and for fine aggregates as 1.0 %.Free (surface moisture) for coarse aggregates is considered nil and for fine aggregates as 2%.

Tests conducted
In this particular experimental study, compressive strength tests are conducted to determine the crushing strength values of various samples of 150 mm X 150mm X 150 mm sizes.All the experimental procedure conforms IS standards.To determine the workability properties, slump flow test, flow table test and compacting factor tests conducted in accordance with standard IS specifications.

General
In all the experimental investigations conducted, primary materials used are ordinary Portland cement, class C and class F fly ash, pulverized fly ash available locally from thermal power plants, substituted with chemical and mineral admixtures.  1, it is evident at very low w/b ratio at 0.25 the compressive strength values shows increasing trend.From 3-days to 56-days curing, for 0% replacement of fly ash and w/b ratio 0.25, the strength gradually increased from 65.5 MPa to 94.7 MPa.Respectively for 50%, 60% and 70% replacement of fly ash, the 3 days strength is very low compared to 3 days strength for 0% fly ash replacement [13].Even the ultimate strength value at 56 days curing a found to be much lower for 50%, 60% and 70% replacement of fly ash.

Materials used in experimental work
At such low w/b ratio of 0.28, use of water reducing super plasticizer or high range water reducer (HRWR) is necessary and it is evident from the observation table [14].The specimens with 50% FA +4% sp show slightly higher strength values compared to 56% replacement of FA.Tests results for 70% FA shows much lesser strength values compare to previous samples and is of nearly 40% lesser.Even though the initial strength values for 56% replacement of fly ash specimens showed lower   The above table highlights utilization of w/b ratio of 0.30 found to be much popular in majority of all experimental investigations.From figure 2 and figure 3, it is observed that low FA content (LAF 0%, 15%, 25%, 45% and 55% FA) shows much higher strength values at a later stage of curing i.e. 180 days compare to all the specimens.Among all the various sample specimens 3-days strength, 7-days strength for HVFA and LFA shows lower values.Considering the 28-days strength for LFA, 90-days strength, 56-days strength and 180-days strength shows higher value [15].In fig.3, LFA specimens with 5% silica fume is represented.Similar to the previous figure, the general trend from early days curing to later days curing, the strength values correspondingly increased.In corporation of 5 % silica fume in all concrete specimens the strength values ranged from nearly 60MPa to nearly 100Mpa.While, the same behaviour s represented for concrete specimens with LFA and HVFA without silica fume content [16].
For w/b ratio for 0.33, very limited literature is available.The 3 days strength for 50% FA is slightly more compare to 7 days strength for 60% FA + 3% sp.It is prominent enough to view 365 days strength for 50% FA and 60% FA+ 3%sp achieved compressive strength around 60 and 70MPa respectively.4 it is observed the compressive strength values gradually increased from 3 days ,7 days , 28 days , 56 days , 90 days and 180 days for 15% FA, 25% FA , 45% FA and 55% FA respectively.Addition of 5% silica fume to 0%, 20% and 40% FA shows immense increasing strength values over the period of 3 days to 180 days curing.From the observation table it can be ascertain that with no content of silica fume or condense silica, fly ash replaced concrete specimens (from 0% to 60%) attains very lower strength even at 365 days curing.

Conclusions
Performance evaluation of physical, mechanical and rheological properties of HVFA concrete with replacement of fly ash with/without additives studied in details.Detailed experimental study reveal, HVFA concrete usually tends to attain minimum early strengths and performs slow at pozzolanic reaction compare to cement concrete.Another striking feature highlights replacement of fly ash beyond 80% by weight fails to develop satisfactory strength and applicable for structures but uses of many additives in HVFA concrete could be possible to achieve improved performance of concrete.
In overall scenario, HVFA concrete shows increasing values in the mechanical properties of including compressive strength, flexural strength, splitting tensile strength and elastic modulus of concrete.Also we can conclude that replacement of FA in concrete great effect on lower drying shrinkage, and higher resistance against chloride, sulphate and acid attacks.For more uses of HVFA concrete need largescaled further studies needed to determine the actual behavior of HVFA concrete in structural aspect.
The review has identified that the nature of the fly ash and additives in concrete, the fineness of fly ash and effect of additives, that determine the mechanical properties of HVFA concrete effectively manner.

Table 4 .
2.1: Detailed List of various materials involved in various experimental investigations

Table 4 .
2.2: Comparison of concrete rheological factors: Fluidity, slump and flow tables values of HVFA Concrete incorporating cement FA and additives According to table 4.2.2, specimens with 50% FA and 4% super plasticizer resulted in very less amount slump and spread value i.e. 65 mm & 440 mm.but other specimens gave satisfactory results with fly ash replacement and super plasticizer.
[12] above table 4.2.2 , it is clearly seen the slump of base concrete with no fly ash is as low as 60 mm and almost no spread.Addition of fly ash improves fluidity of concrete and possesses effective way on improving the plasticity of concrete[12].Hence with increasing fly ash dosage the fluidity is improved accordingly.
Previous experimental studies prominently highlight use of w/b ratio 0.4.Extensive experiments are conducted taking 0.4 w/b ratio.From the fig.