Self-Curing Concrete for the Indian Construction Industry

Dr. Dada S. Patil & Dr. Fauwaz A. M. Parkar, Civil Engineering Department in Anjuman-I-Islam’s Kalsekar Technical Campus, School of Engineering & Technology, Panvel, Navi Mumbai

Introduction

The desired performance of concrete in the long run depends on the extent and effectiveness of curing [1 & 2]. In the Indian construction sector, curing concrete at an early age is a problematic issue because of lack of awareness or other unavoidable circumstances prevailing on concrete construction sites. A Google form was circulated among civil engineering fraternity in India. It comprised of people belonging to academia (civil engineering teachers), builder firms, client organizations, consultancy firms, contracting firms, Government establishments, RMC plants, research & development set ups and others (MEP, manufacturing companies, sales & service, valuation, interior designing, etc). The concept of Self-Curing (SCu), also known as Internal Curing, was briefly explained in the Google form for the respondents to refer before filing the questionnaire form.

Curing of Concrete

Curing is a mechanism of governing the movement of moisture from the concrete body while hydration of cement takes place. If optimum properties of concrete need to be attained, it must be adequately cured. For effective cement hydration, there must be enough supply of moisture to the concrete. This facilitates in decreasing the porosity to a possible minimum extent so that the required strength as well as durability can be achieved, thereby leading to a reduction in concrete volume change because of shrinkage [3]. As the products of cement hydration fill the capillaries and pores either partly or completely, adequate curing reduces the paste porosity [1-3]. Even if higher water-cement ratio is adopted, accelerated evaporation of water takes place for the concrete placed in an arid region, leading to a decline in the initial water-cement ratio. It results in an interrupted hydration of cement particles, thus affecting the quality of concrete to a large extent [4].

Shortcomings of Age-Old Curing Methods

The various modes of external curing techniques have many shortcomings such as acute shortage of potable water, structures in remote places, low water-cement ratio of High Performance Concrete (HPC), etc. As far as Indian construction sector is concerned, external curing methods are complex and labor-dependent. Many labors do not understand the importance of curing the concrete thoroughly for a specified period of time. On the contrary, sometimes, they may over-cure the concrete leading to a water wastage through run-off and evaporation.

Water Scarcity v/s Colossal Wastage of Water for Concrete Curing

For producing 1 cubic meter of hardened concrete, approximately 3 cubic meter of water is required. Major part of this water is consumed for the curing purpose [5]. A huge amount of water being utilized by human beings has led to the ecological imbalance in terms of water availability. Nation Water Mission and Nation Action Plan for Climate Change (NAPCC) have set a goal of enhancing the efficiency of water utilization in India by 20% [6].

Figure 1 depicts huge amount of water being utilized for the concrete curing. On the other hand, figure 2 shows the suffering of Indian citizens due to water scarcity.

Self-Curing Concrete (SCuC) or Internally-Cured Concrete

The rate of cement hydration slows down in the absence of enough moisture inside the concrete mass. When the internal Relative Humidity (RH) within the pores falls below 80%, mechanism of hydration practically stops and when it drops to 30%, hydration becomes almost negligible [7]. Enough calcium silicate hydrate (C-S-H) does not get formed if the hydration process ceases [8]. To retain enough moisture inside the concrete, Self-Curing can be practiced. It is especially recommended for the concretes having low water-cement ratio due to chemical shrinkage associated with Portland cement hydration and lesser permeability of these materials not allowing curing water to penetrate enough depth. A hydrophilic material such as Super Absorbent Polymer (SAP) can be used as SCu additive [7]. These water absorbing polymers, classified as hydro gels, when cross-linked, absorb aqueous solutions through hydrogen bonding with water molecules. The other hydrophilic materials, used as Self-Curing agents, are Shrinkage Reducing Admixtures (SRA) such as propylene glycol, polyethylene glycol, paraffin wax, polyvinyl alcohol, acrylic acid, etc. [9]. These are incorporated by mass of cement to suppress the surface tension of mixing water. These polymers tend to create hydrogen bonds with water molecules and decrease their chemical potential. This leads to reduction in vapor pressure, thereby declining the evaporation rate from the concrete and improving hydration of cement particles [10].

The different Lightweight Aggregates (LWAs) used in prewetted condition for SCu are pumice, expanded shale, expanded clay, sintered fly ash aggregates, perlite, etc. [9]. These are incorporated as a part volumetric replacement of coarse aggregates or fine aggregates. They give out water gradually to maintain the sufficient moisture condition inside the concrete mass. SCu facilitates in reducing self-desiccation, autogenous shrinkage, shrinkage cracking, plastic shrinkage cracking and water absorption [11]. In external curing, depth of water penetration is governed by concrete quality and age; however, water is uniformly distributed throughout the concrete mass in SCu concrete.

Google Form Survey about Awareness and Implementation of Self-Curing Concrete

Various questions about SCuC were asked in the Google form and the answers were sought in terms of selecting any one option among the various options provided for every question. The overall responses received were 226. However, the number of responses for various questions varied because no question was made compulsory.

Type of Organization: Overall 225 Responses

Figure 3 shows the responses for the type of organization. From “academia”, there were 58 responses (25.8%). From “builder” set up, there were 16 responses (7.11%). People responding from “client organizations” were 19 (8.4%). “Consultancy firm” responses were 46 (20.4%). “Contracting firm” contributed 45 responses (20%). Only 8 responses (3.55%) were received from “Government engineers”. 10 engineers (4.44%) from “RMC plant” responded.


From “R & D” domain, only 2 people (0.88%) responded. From “others category”, there were 21 (9.33%) entries.

Size of Organization: Number of Employees - Tiny : ≤ 50; Medium Sized: 51 to 249 and Big Sized: ≥ 250: Overall 221 Responses

Size of organization is depicted in figure 4. There were 221 responses. 25 responses belonged to “tiny” organization. From “medium sized” organization, 115 responses were recorded and from “big sized” organization, 81 people responded.


Working Experience in Years: Overall 221 Responses

Figure 5 shows working experience of the responders. 112 people were having experience ranging from “1 to 5 years”. 50 entries were for “6 to 10 years” experience. 28 people had “11 to 20 years” of experience. 29 people belonged to “21 to 40 years” experience. Only 2 (0.89%) had an experience of “41 years and more”.


What was the initial source through which you came to know about Self-Curing concrete?: Overall 222 Responses

Referring figure 6, “Internet” was the initial source for 66 people (29.7%). “Media” was the source for 14 responders (6.3%). “Technical articles” were the source for 59 people (26.6%). For 12 people (5.4%), it was “STTP/Workshop”. For 23 people (10.4%), “webinar/seminar” was the source. 16 people (7.2%) did “own research” about SCuC. It’s somewhat encouraging to note that 12 civil engineers (5.4%) are “using SCuC on site”. 21 people (9.4%) had “no idea” about SCuC


When was the last time you used Self-Curing technique to cure the concrete in laboratory or on site?: Overall 224 Responses

Referring figure 7, SCu technique was used by 15 persons (6.8%) “during last 6 months”. 9 people (4%) used it “more than 6 months ago”. 30 people (13.5%) utilized SCuC “more than a year ago”. However, 169 people (75.8%) “did not use” SCuC at all.


Would you recommend specifying & implementing Self-Curing in HPC?: Overall 222 Responses

Referring figure 8, it is “very likely” that 55 respondents (24.8%) would specify and implement SCuC in HPC. “Likely” was the response by 105 people (47.3%). “Less likely” was the option chosen by 17 respondents (7.6%). 5 participants (2.25%) aired their opinion as “No”. However, 40 participants (18%) had “no idea”.


Which method of curing you would like to adopt for HPC?: Overall 217 Responses

Referring figure 9, “Spraying” was the choice by 45 respondents (20.7%). “Immersion” was preferred by 25 participants (11.5%). 38 people (17.5%) would like to adopt “membrane” curing. 109 participants (50.2%) had “Self-Curing” as their choice.


Rate the benefits of Self-Curing on 1 to 5 Likert Scales (1- not beneficial; 2- slightly beneficial; 3-moderately beneficial; 4- beneficial and 5- highly beneficial): Overall 218 Responses

Only 2 participants (0.9%) felt that it’s not beneficial; whereas, according to 77 respondents (35.3%), it’s highly beneficial. Figure 10 shows the graphical presentation.

Analysis of Google Form Survey for Each Type of Organization

In this section, detailed analysis of Google form survey is carried out in tabular form for each type of organization and relevant discussion is done. For each question, attributes with highest responses are only discussed. Other responses can be referred from the tables.

Academia: 58 Responses

Years of experience (56 responses): 1 to 5 yrs. - 11; 6 to 10 yrs. - 18; 11 to 20 yrs. - 15 and 21 to 40 yrs. - 12

Size of organization (58 responses): Tiny- 4, medium sized – 34 and big sized – 20


Referring table 1, initial source of knowing about SCuC for 26 civil engineering teachers (44.82%) were technical articles. 46 teachers (79.31%) did not use SCuC at all. This clearly indicates that they need to show keen interest in SCuC concept and also encourage students to carry out projects related to SCuC. Any initiative for alternative techniques shall typically start from an academic set-up and gradually spread to the industry for better technical understanding. 33 academicians (58.89%) indicated “likely” possibility of specifying and implementing SCu in HPC. However, responses for “very likely” were 14. For HPC, the method of curing which academicians would like to adopt is “Self-Curing”, owing to 26 responses (45.61%) for this curing mode. SCuC is beneficial as per 29 academicians (50%).

Builder Organizations: 16 Responses

Years of experience (16 responses): 1 to 5 yrs. -10; 6 to 10 yrs. - 4; 11 to 20 yrs. -1 & 21 to 40 yrs. -1

Size of organization (16 Responses): Tiny- 2, medium sized - 12 and big sized – 2


Referring table 2, it’s a positive indication that 2 responders are using SCuC on their sites. However, there is a possibility that curing compounds applied on the concrete surface might have been mistaken as SCu technique; though it was made clear in the Google form that the survey is not about curing compounds. 13 civil engineers (81.25%) have not used SCu technique at all. This shows that they are habituated to the conventional methods of curing. 9 participants (60%) would “likely” recommend specifying and implementing SCu in HPC. Spraying and SCu are the curing methods preferred for HPC by 6 respondents (40%). 5 people (35.71%) think that SCu is moderately beneficial.

Client Organizations: 19 Responses

Years of experience (19 responses): 1 to 5 yrs. - 12; 6 to 10 yrs. - 5 and 11 to 20 yrs. - 2

Size of organization (19 responses): Tiny- 0, medium sized -5 and big sized -14


From table 3, it can be seen that for 7 people (36.84%), technical articles were the initial source to know about SCuC. 13 respondents (68.42%) did not use SCu technique at all. However, it was encouraging that 10 participants (52.63%) would “very likely” recommend SCu in HPC. Self-Curing would be preferred to cure the concrete by 10 respondents (52.63%). 11 engineers (57.89%) think that SCu is beneficial.

Consultancy Firms: 46 Responses

Years of experience (46 responses): 1 to 5 yrs. - 26; 6 to 10 yrs.-13; 11 to 20 yrs. - 3; 21 to 40 yrs. - 3 and 41 & more yrs. -1

Size of organization (46 responses): Tiny- 8, medium sized - 20 and big sized -18


As shown in table 4, internet was the source for getting known about SCuC for 18 respondents (39.13%). There were 37 engineers (82.22%) who never specified SCuC to be used on the site. 19 consulting engineers (42.22%) would “likely” recommend SCu in HPC. SCu would be adopted by 24 people (54.54%) to cure HPC. SCu is deemed to be beneficial by 21 participants (46.67%).

Contracting Firms: 45 Responses

Years of experience (45 responses): 1 to 5 yrs. - 32; 6 to 10 yrs. -7; 11 to 20 yrs. - 2; 21 to 40 yrs. - 3 and 41 & more yrs. -1

Size of organization (45 responses): Tiny- 9, medium sized - 22 and big sized - 14


Referring table 5, internet was the initial source for 17 participants (38.63%) to get acquainted with SCuC. 32 civil engineers (72.72%) of contracting firms did not use SCuC technique at all. This indicates that an awareness about SCuC is needed among contracting firms to ripe its benefits. 22 engineers (51.16%) would “likely” recommend SCu in HPC. SCu would be the preferred way of curing HPC for 24 (55.81%) respondents. 19 participants (45.23%) looked at SCu as highly beneficial.

Government Establishments: 8 Responses

Years of experience (8 responses): 1 to 5 yrs. - 2; 11 to 20 yrs. - 3 and 21 to 40 yrs. - 3

Size of organization (8 responses): Tiny- 0, medium sized - 5 and big sized - 3


From table 6, it can be seen that internet, technical articles, using on site, media and having no idea were responses for the initial awareness of SCuC. 6 Government engineers (75%) did not use SCu technique at all. 5 (62.5%) engineers would “likely” recommend SCu for HPC. SCu would be adopted by 3 respondents (37.5%). SCu was thought to be highly beneficial by 4 participants (50%).

Ready-Mixed Concrete Plants: 10 Responses

Years of experience (10 responses): 1 to 5 yrs. - 7; 6 to 10 yrs. - 1 and 21 to 40 yrs. - 2

Size of organization (10 responses): Tiny- 1, medium sized - 6 and big sized – 3


As per table 7, the initial sources for the SCuC awareness were media, technical articles, webinar/seminar, own research and by using on site. Some had no idea about the concept. 4 people (44.44%) did not use SCu method at all. 4 RMC plant engineers (40%) had no idea about whether to recommend SCuC or not. Self-Curing would be adopted by 5 respondents (55.56%). SCu was deemed to be highly beneficial by 6 participants (66.67%).

Research and Development Organizations: 2 Responses Years of experience (2 responses): 1 to 5 yrs. - 1 and 21 to 40 yrs. - 1

Size of organization (2 responses): Medium sized -1 and big sized -1

Only 2 responses were received from Research and Development organizations as shown in table 8.


Others (MEP, manufacturing company, sales & service, etc.): 21 Responses

Years of experience (18 responses): 1 to 5 yrs. - 11; 6 to 10 yrs. - 2; 11 to 20 yrs. - 2 and 21 to 40 yrs. - 3

Size of organization (16 responses): Tiny- 1, medium sized - 10 and big sized - 5


Table 9 reveals that internet and technical articles were major sources of knowing about SCuC at 26.31%. SCu method was not used at all by 15 people (71.43%). Recommending SCu for HPC would be “likely” by 9 respondents (42.85%). Self-Curing would be preferred by 11 people (57.89%). SCu was thought to be beneficial by 12 engineers (60%).

Summary and Conclusions

Though the human resources working in civil engineering fraternity have acquired some awareness about the concept of SCu, negligibly few have used the technique to cure the concrete. Most of them have not used internal curing at all. “Very likely” recommendation of SCu is still not the first choice.

Construction sector is next largest contributor to the Indian economy after agricultural domain. Hence, it needs to be prioritized for creating world-class infrastructure as well as finishing projects well within the deadlines. In India, water availability in required quantity and quality is a problematic issue on many sites. Due to rapid urban development, infrastructure has been growing fast. Water availability per capita has declined considerably because of improper usage or lack of knowledge about the efficient usage of water.

Apart from avoiding wastage of enormous amount of water, SCu also facilitates in distributing moisture uniformly inside the mass of concrete which other curing methods fail to achieve, especially in HPC with low water-cement ratio. India has a complicated physical diversity in terms of temperatures and humidities across various states. These parameters are vital for concrete performance in its life cycle. Mere awareness and experimental work about SCuC in the laboratory are not sufficient. A paradigm shift is needed to study the fresh and hardened properties of SCuC in the field conditions to check its feasibility as an effective solution for the concrete curing. A large-scale awareness and practical implementation of internal curing of concrete in India would result in a sustainable development.

References

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About the Authors

Dr. Dada S. Patil is Associate Professor in Civil Engineering Department in Anjuman-I-Islam’s Kalsekar Technical Campus, School of Engineering & Technology, Panvel, Navi Mumbai. His areas of interest are Concrete Technology, Self-Curing Concrete, Repairs & Rehabilitation of Structures, Structural Analysis & Design and Geotechnical Engineering. He can be reached on: This email address is being protected from spambots. You need JavaScript enabled to view it..

Dr. Fauwaz A. M. Parkar is Associate Professor & Head of Department of Civil Engineering in Anjuman-I-Islam’s Kalsekar Technical Campus, School of Engineering & Technology, Panvel, Navi Mumbai. His areas of interest are Affordable Housing, Construction Engineering & Management, BIM, GIS, Planning & Scheduling and Project Management. He can be reached on: This email address is being protected from spambots. You need JavaScript enabled to view it.