Admixture-based self-compacted concrete with self-curing concrete techniques a state of art of review

1. Introduction

Concrete is one of the most consumed and cheapest materials in construction field among all other materials. The urge of demand for the concrete in construction and industrial field made the researchers to develop the high performing concrete with more feasibility (Prakash et al., 2021). Having such requirements has an objective several types special concretes were developed; out which self-compacting concrete satisfied most of the construction needs. More over the SCC had attracted the attention of most of the researchers because of the several benefits over Normally Vibrated concrete (NVC) (Singh et al., 2019). It enhances the working environment of construction field by avoiding the usages of vibrator for filling up the formwork in congested reinforced structures and also avoids enormous amount of noise pollution (Kostrzanowska-Siedlarz and Gołaszewski, 2016). The productivity and outcome improves due to faster, easy and perfect finishing during the filling of formwork. The major drawback of SCC is usage of more fines in developing the concrete; this can be counteracted by using partial or complete replacement of cement, fine aggregate and coarse aggregate with pozzolanic materials. Since SCC does not require any vibrators for extracting the voids in the concrete mix, it is very important to pack the concrete efficiently to avoid voids. So, using binary and tertiary binder and partial replacement of fine aggregate can produce the efficient packing of concrete. SCC has major advantage while designing complex reinforced concrete structures, which helps in filling up the formwork effectively. The SCC was first developed by Professor. H. Okamura (Okamura and Ouchi, 2003) (Ouchi, 1998) paved the way for more exploration in this field of SCC because of its several advantages. To optimize the efficiency of SCC several components were considered; such as binder content, quantity of fine aggregate and coarse aggregate, chemical admixtures and other composite materials, that influences the optimization of SCC.

2. Impact of shape of mineral admixture and aggregates over SCC

Fly ash is one of the major pozzolan plays a vital role in developing the high strength, high performance, economical concrete and also a eco-friendly geopolymer concrete. Fly ash is a waste material obtained from thermal power plant during combustion of pulverized coal because of the pozzolanic properties it can be replaced with the cement. It can make our environment green by reducing the CO2 and saving the large amount of land area from dumping these finer pozzolanic materials. It is estimated that annually 300–500 million tons of fly ash produced around the globe (Singh et al., 2019). Electricity produced through lignite power station serves to be most efficient, economic and less hazardous, while compared with nuclear power stations (Kopytko and Perkins, 2011) as shown in Fig. 1. By incorporating/regulating the solid waste disposals from lignite based power stations more efficient and durable construction materials can be produced (U.S. Environmental Protection Agency, 2014). Depending upon the types of coals burnt, chemical compositions, collection of ashes from different layers from chimneys, electrostatic precipitators and other filtering materials used fly ashes can be classified into different types shown in Table 1. Adding of Fly ash improves the flexural behaviour of concrete by making the concrete well packed. The denser interfacial transition zone (ITZ) because of higher packing factor helps in obtaining stronger bond. It also helped in attaining the higher critical stress intensity factor (Sarker et al., 2013). The critical stress intensity factor was highly influenced by the incorporation of finer material making the concrete composite matrix more denser (Benarbia and Benguediab, 2015). Shape, size and chemical composition of material plays an important role in attaining the ideal self-compacting concrete. The durability properties of the fly ash aggregate concrete indicate that the performance is satisfactory for structural application.

Table 1. Types of fly ash based on the chemical composition (Nguyen et al., 2019).

Chemical compositions (% by weight)	OPC	F-class fly ash	C-class fly ash	Standard fly ash	EA expansive additive.
SiO2	19.70	61.09	35.71	26.61	2.12
Al2O3	5.19	20.35	20.44	13.60	4.75
Fe2O3	3.34	5.20	15.54	18.34	0.14
CaO	64.80	2.32	16.52	24.97	61.19
MgO	1.20	1.35	2.00	2.33	0.73
Na2O	0.16	0.79	1.15	1.75	–
K2O	0.44	1.36	2.41	1.77	–
SO3	2.54	0.28	4.26	8.53	26.46
Free lime	0.87	0.03	1.71	3.93	28.94
LOI	2.10	5.68	0.49	0.53	4.48

Incorporating various sizes of the aggregates in the mix increases the packing efficiency of the concrete and also results in better performance. Fig. 2 and Fig. 3 show the SEM images of various size and shapes of the aggregate. The packing efficiency and the flowability are highly influenced by the shape of variables used (Binders and aggregates) (Khayat, 2015). From the Scanning Electron Microscope image of Fig. 1 the SEM images of fly ash particles are shown in the Fig. 3 (a) and (b), from the figure it is clearly seen that the shape of the fly ash is spherical. This is the key influencing factor in enhancing the workability of the concrete and reducing the water/binder ratio. In SCC the major drawback is excess usage of binder content (>450 kg/m3) (Hassan and Mayo, 2014) but this gives better flowability. Since binder content serves as the medium in which aggregates are suspended in it, higher binder content will enhance the rheological properties.

Usage of high cement content affects the durability and mechanical properties of concrete (Buenfeld and Okundi, 1998) such as; increases shrinkage, affects the carbonation rate, fails in chloride penetration test, leads to uneconomical structure, etc. The study has been carried out replacing cement by mineral admixtures such as fly ash, micro silica, metakaolin, bentonite and ground granulated blast-furnace slag (GGBS) up to 60% without using alkaline solution. Addition of mineral admixture up to 30%–40% enhances the rheological, durability and mechanical properties of concrete. It also reduces the usage of cement content making the concrete highly economical (Yazici, 2008). Inorganic aluminosilicate polymer uses waste fly ash as source material instead of cement in concrete. The compressive strength of 25–80 MPa can be obtained, with the densities ranging between 1600–2019 kg/m3 (Athiyamaan and Ganesh, 2017). Table 2 shows the evolution of SCC mix designs with respective to their variables (Influencing factors) and responses (Mechanical Properties).

Table 2. Typical design method statistical modelling on SCC.

Author	Design Type	Influencing Factor (Independent Variable)		Responses (Dependent Variable)
Author	Design Type	Content	Ranges	Responses (Dependent Variable)
Sonebi (2004)	Statistical Method 2k Factorial Design, polynomial regression	W/P	0.38 to 0.72	Filling and passing abilities, segregation and compressive strength
		Cement content	60–216 kg/m3
		PFA	183–317 kg/m3
		SP, by mass of powder	0%–1%
Khayat et al. (1999)	Statistical Modelling: Factorial design	viscosity-enhancing agent,	240 l/m3–400 l/m3	Filling and passing abilities, segregation.
		high-range water reducer,	0.3 to 1.1
		water-to-cementitious materials ratio,	0.37%–0.50%
		volume of coarse aggregate,	240 kg/m3 to 400 kg/m3
		Cement Content.	360 kg/m3 to 600 kg/m3
Nehdi et al. (2001)	Artificial Neural Networks	Slump-flow, Filling and passing abilities, segregation and compressive strength		Rheological properties and Compressive strength
Bouziani (2013)	Factorial and response surface designs. Ternary contour plots	River Sand (RS, 5 mm)	848 kg/m3 (21 mixes of 20%, 40%, 60%, 80% and 100%) replacement	Compressive strength and flowing ability.
		Crushed Sand (CS, 4 mm)
		Dune Sand (DS)
		Cement	380 kg/m3
		Marble waste powder	199 kg/m3
		Gravel (10 mm)	880 kg/m3
Barrak et al. (2009)	variance analysis, binary tree method coupled with the bootstrap technique	viscosity-enhancing agent	3%–4.5% of the mass Total Cementitious Material	Rheological Properties of cement paste
		high-range water reducer	0.9%–1.1% of the mass Total Cementitious Material
		water-to-cementitious materials ratio,	0.29 to 0.33
		Volume of coarse aggregate,	Nil
		Cement	480–500 kg/m3 CEM I 52,5 N CP2
		Limestone filler	20%–30% of mass of Cement
Asteris et al. (2019)	surrogate models - (MARS) and M5P model tree	Cement	209.5–550 kg/m3	Rheological and Mechanical Properties (28 days compressive strength)
		Coarse aggregate to fine aggregate ratio	0.47 to 2.6 (Size 6.7 mm–30 mm)
		Metakaolin	0–163.5 kg/m3
		Binder to water ratio	0.27%–0.6%
Okamura and Ozawa (1996)	Traditional – Volume based empirical method	Coarse aggregate	50% of the solid volume	Rheological and Mechanical properties
		Fine aggregate	40% of the mortar volume
		water-powder ratio	0.9 to 1.0
Nan Su et al., 2001	Packing Model - mix design method	Cement content	200 to 350	Slump flow, V-funnel, L-flow, U-box and compressive strength
		Fly ash	142 to 157
		GGBS	61 to 67
		Water Content	170 to 176
		Fine aggregate	912 to 961
		Coarse aggregate	706 to 743

3. Overview on Self Curing Concrete

The comparative study between concretes of different internal curing agents to that of fully cured concrete shows that the hardships faced due to lack of proper resources for external curing can be overcome without compromising on the workability or strength of the SCC. From this, it is understood that the self-curing agents prove to give results equivalent to that of the fully cured concrete and in some durability cases shows superior performance (Rampradheep et al., 2017).

Rampradheep (et. at) carried out an experiment study on effect of raphanussativua (raddish) based component as a self-curing agent in SCC. Initially the concrete was casted with basic ingredients of OPC 53 grade that confirms to IS: 12269-2013 (IS 12269: 2013, 2013), Class F Fly ash based on ASTM C 618 and aggregates that confirm to IS: 383–1970 (IS 383 (1970), 1970). The internal curing agents like Poly-Ethylene Glycol, Super Absorbent Polymers, Light Weight Aggregate, External Coating, Liquid Paraffin Wax and extract from radish were used. The comparative study between self-cured (SC) and normally cured (NC) mechanical and rheological properties explained detailed in Table 3. The optimized usage of hydrophilic (PEG 4000) and hydrophobic (LPW Light) chemicals as a self-curing agent's enhanced the performance of SCC especially in hot region (50 °C) by reducing the evaporation, leaving optimum water content for hydration process as seen in SEM image of Fig. 4 and Fig. 5, As a result the strength of self-curing concrete can be increased by 20%–30% (Madduru et al., 2018).

Table 3. Significant studies on Self Curing Concrete.

Name of the author	Curing Agent	Mix design Proportion		Description
Name of the author	Curing Agent	Ingredient	Kg/m3	Description
Rizzuto et al. (2020)	Poly-Ethylene Glycol 400 (PEG - 400) – 1.5% of water/binder	1. Cement	450	The comparative study of mechanical properties of Self cured (SC) Vs Normally cured (NC) concrete was carried out for different temperature ranging between (25 °C to 50 °C).SC showed 20%–25% better mechanical properties than NC concrete.
		2. Mineral admixture	–
		3. Fine aggregate	614
		4. Coarse aggregate	1172
		5. Chemical admixture.	–
		6. Water/binder	0.4
Rama et al. (2020)	Polyethylene glycol (PEG)-4000 Liquid paraffin wax light (LPW)	1. Cement	500	The comparative study of normal curing (N.C), water curing (W.C) and self-curing with polyethylene glycol (PEG) and liquid paraffin wax (LPW) was carried out. Self-cured concrete shows better mechanical properties than N.C concrete and performed equally with W.C concrete.
		2. Fine aggregate	800
		3. Coarse aggregate	77
		4. Water	190
		5. Fly Ash	110
		6. Micro Silica	40
		7. Super plasticizer	6
Obulesh et al. (2020)	Super Absorbed Polymer (SAP)	1. Cement	370	The comparative study between normal concrete and self-curing concrete by using SAP of percentages 0.1%, 0.2%, 0.3% showed that self-curing concrete showed better mechanical properties than normal concrete.
		2. Coarse Aggregates	1283.63
		3. Fine Aggregates	698.28
		4. Liquid/Water	148.8
Alaa M.Rashad	Lightweight Expanded Clay Aggregate (LECA)	1. Cement	413.33	The Comparative study between that of self-cured concrete and reference concrete showed that the use of LECA as self-curing agent improved the mechanical properties
		2. Coarse Aggregates	681.5908
		3. Fine Aggregates	1187.33
		4. Water	186
Shen et al. (2015)	Super Absorbent Polymers (SAP)	1. Cement	512	The IRH of concrete that was internally cured with SAPs increased with the increase of IC water content 28 days after casting under both sealed and unsealed conditions. The critical time of the IRH in internally cured concrete increased with IC water content under sealed and unsealed conditions.
		2. Coarse Aggregates	1131
		3. Fine Aggregates	636
		4. Water	171
		5. Super Plasticizer	3.6
Liu et al. (2017)	Cenospheres	1. Cement	592	The perforated cenospheres show good water absorption rate. At early age, Perforated cenospheres used as an internal curing agent in cement mortar mixture resulted in slightly lower strength but with progress in hydration the compressive strength was higher than the ones without internal curing.
Liu et al. (2017)	Cenospheres	2. Water	207.2

4. Literature survey on SCC

Ebrahim Sharifi et at conducted a detailed research on optimization of SCC by considering the significant parameters that influences the properties of SCC Taguchi optimization technique was adopted to study the properties of SCC. The adopted method showed a significant improvement when compared with decision maker's estimated mixture design. Out of all variables Cement (Binder content), water to cement ratio and mixing time was found to the significant parameters affecting the concrete mix design. The optimum cement, water to cement ratio, SP, coarse aggregate to fine aggregate content and mixing time were found to be 425 kg/m3, 120 kg/m3, 0.35%, 0.60%, kg/m3 and 120 s (Sharifi et al., 2020).

Chandra sekhar reddy idukuri et al (2019) carried out an experiment on effect of graphene oxide on microstructure and strengthened properties of fly ash and silica fume based cement type −1, class-F fly ash and the polycarboxylate graphene super plasticizer etc. The graphene oxide used in this work was extracted from graphite by hummer method and finally, the obtained graphene oxide (GO) solution concentration was controlled as 0.3%. The replacement of cement with silica fumes by 1%, 2%, and 3% later they had prepared cement composition, for cement composition they had taken 450 kg of cement, 162 kg of water, 1.2 g of polycarboxylate super plasticizer and varied quantities of graphene oxide. After knowing the structural characterization of graphene oxide, finally it is confirmed that by the cross-linking interaction of graphene oxide, nano sheets and calcium ions, aggregation of graphene oxide had happened in the cement paste. At last is had been concluded that an improved dispersion of graphene oxide nanosheets was offered by the incorporation of silica fume at 3% and 5% in the graphene oxide cement paste. By replacing maximum 15% of fly ash in graphene oxide cement paste, the preliminary fluidity was obtained as 265 mm later it increase the fluxeral strength up to 65.24% at 0.04% of graphene oxide (Sekhar et al., 2019).

S.K.Malahotra et al (1999) investigated on the effect of addition of fly ash and burnt clay pozzolana on certain engineering properties of cement composites. In this research they had used different types of mortar and later they developed modified composite mortar, due to the utilization of pozzolanic material they accelerated test known as lime reactivity test. In this research the mix design was followed as per Indian standards. And the activity of a pozzolana is represented by its compressive strength. Similarly they had evaluated the properties of all the materials using in this project. Preparations of modified composite mortors are methods of testing, bond strength, water retention and compressive strength. They had casted cubes and cured it for 7 days and for one year. They have achieved compressive strength on 5 cm cubes at 110+-5% and 2 °C temperature and relative humidity is 95%, finally the average results had been taken. The result helps to predict the definite relationship between the reactivity of pozzolana and the increase in strength i.e., higher the lime reactivity of the pozzolanic material, higher will be the strength (Malhotra and Dave, 1999).

Dr. K. Pandurangan et al (2017) carried out studies on effect of source of fly ash on bond strength of geopolymer concrete, this research is done to understand the difference between the ordinary concrete bond behaviour to geopolymer concrete under various composition of fly ash and GGBS including the alkaline solution. They have carried out pull out as per IS 2770 part 1 standards. They have done comparative analysis between geopolymer concrete and conventional. It gives 5 times higher than the value given in IS 456: 2000 specified for the conventional concrete. Strength will increase with decreasing the fly ash (Pandurangan et al., 2018).

Manu S. Nadesan et al (2017) carried out an experiment on structural concrete using sintered fly ash light weight aggregate. The qualities of the sintered fly ash aggregate are superior to normal aggregate concrete. They observed the chemical interactions i.e., if ITZ of sintered fly ash aggregates, sintered temperature increases pozzolanic reactivity between the aggregate and paste also increases. This research is carried out mainly to increase the strength of the concrete by reusing the waste materials (Nadesan and Dinakar, 2017).

T. Raghavendra. et al (2015) carried out an experimental study on engineering properties of controlled low strength materials using fly ash and waste gypsum wall boards. In this research they have used replacing materials of industrial by products, construction and demolition wastes namely fly ash, waste gypsum boards as secondary cementitious materials in CLSM is recommended. This helps to reduce air pollution and large usage of cement. This research is mainly carried out on the basis of sustainability concept and low cost. They have concluded, since replacing waste gypsum and fly ash in cement it will increase the strength, durability and also binding property (Raghavendra and Udayashankar, 2015).

Shaik Hussain et al (2017) carried out a research on comparative study of accelerated carbonation of plain cement and fly ash concrete. They got to know by this research is the mechanical properties of concrete increases with increasing the duration of carbonation, elastic modulus has decreased for fly ash concrete compare to plain cement concrete, the depth of the carbonation will also increase and when designed for same water binder ratio the concrete with higher strength where cement is partially replaced by fly ash has shown similar resistance against the plain cement concrete (Hussain et al., 2017).

Anuja narayanan et al (2016) carried out an experiment investigation on fly ash based geopolymer mortar under different curing regime for thermal analysis, class F type fly ash is has more strength than class C type fly ash. The alkaline liquid preferably used for geopolymer concrete may be sodium hydroxide or potassium hydroxide and sodium silicate or potassium silicate, 10 M concentration is used throughout the process. The oxide composition of class F fly ash is determined using X-ray fluorescence test. Two types of mixing are carried out such as conventional and 20.01 Mpa, 23.56 Mpa and 29.27 Mpa for 1,7,14, and 28 days of compressive strength. Finally they have concluded 100% replacement of cement with fly ash found capable of increasing the dry density by 2.83% and 8.59% for cured specimen and for hot specimen it is reduced dry density by 5.31%, thermal conductivity decreases upto 27%, 37% and 60% for specimen in autoclave(Narayanan and Shanmugasundaram, 2017).

F. N. Okoye et al (2015) carried out research on mechanical properties of alkali activated fly ash/kaolin based geopolymer concrete. The strength development of fly ash and kaolin based geopolymer concrete compared favourably with OPC concrete. Compressive strength will fly ash compared to OPC. The preparation of geopolymer did not required OPC. Hence, the green house emission could be reduced(Okoye et al., 2015).

5. Conclusion

The literature review portrays the need for research in the field of SCC, since there is no common mix design or procedure for predicting the exact mix proportions for the fixed target strength. The literature survey helps to identify and refer several optimization techniques that can enhance the performance of SCC by incorporating self-technique.

It was identified that the variables such as binders, fine aggregate, coarse aggregate, W/C ratio, Packing density factor and HRWR were the key parameters in influencing the rheological and mechanical properties of SCC.

It was identified that the compressive strength between 23.12 and 74 MPa has the respective density ranging between 1651 and 2017 kg/m3, showing the correlation between strength and density. The strength development of Fly ash and kaolin based SCC had high performance and better durability when compared with conventional OPC concrete.

Fly ash concrete mixes with higher water-binder ratios have shown a higher rate of carbonation when compared to that of plain cement concrete because of higher penetrability of the matrix which is due to the lack of calcium hydroxides in the fly ash mixes.

It is possible to produce concrete having the tensile strength and elastic modulus varied from 2 MPa to 4.9 MPa and 16.7–30.65 GPa respectively. Self-curing concrete improves the strength and efficiency of upto 20%. The current study says that the bending of special concretes can prevent the consumption of non-renewable natural resources. The structural efficiencies of these concretes are much higher than the conventional normal density concretes. Hence the future study is to develop a statistical model and proper mix design proportion by blending the self-curing technique in SCC. The generated database will be advantageous for selection of best innovative material for production of good nature of SCC and additionally for further research work in this specific area.

Acknowledgement

The article would not have been possible without the exceptional support of my institute BMS Institute of Technology and Management, Bangalore, India for their continuous support.