Built Expressions Bangalore :: Smart Dynamic Concrete

Comments (0)

Comments This Article

SMART DYNAMIC CONCRETE

Innovative Concept For Mass Housing Concrete Applications

Shivram B Bagade1, Bruno D’Souza2

1Scientist, A-EBA, DCAS, BASF Construction Chemicals Asia Pacific 300 Jiang Xin Sha Road, 200137 Pudong, Shanghai, P. R. China shivram.bagade@basf.com

2Regional Business Segment Manager, Admixtures, Asia Pacific

BASF South East Asia Pte Ltd, 33 Tuas Ave 11, Singapore 639090

bruno.dsouza@basf.com

Abstract: Constructing fully-fledged and pre-engineered houses is a relatively new concept in India. It is estimated that India needs more than 27 million urban houses. Better understanding of concrete has resulted in more effective use of available raw materials & resources. Therefore, nowadays specifications are clear and well defined. Developments are occurring in the utilization of modern formwork, ready-mixed concrete and admixtures. Projects are fast tracked where economics on the investment in formwork is carefully evaluated. With a new and innovative Superplasticiser and Viscosity Modifying Agent (VMA) it’s now possible to achieve formerly unseen stability & robustness levels in SCC mixes, despite low fines contents. Such admixtures can make ordinary concrete extraordinary and meet some of the challenges faced in Mass Housing projects. In this paper the authors will set out to explain the benefits of Smart Dynamic Concrete and its use in a Slum Clearance project in Bengaluru.

Keywords: cement, chemical admixtures, SCMs, VMA, SCC, slum clearance projects, fast track, mass housing, Sustainability

INTRODUCTION

"Shelter is a basic need of human beings, from the beginning of civilization". Rapid transition in science and technology creates several challenges for planning, development and operation of cities. These challenges lead to experiments with new approaches to the governance, design, construction and finance of urban infrastructure and services making our cities smart. India’s population is 1,241,491,960 and comprises 28 States and 7 Union Territories. About 30 people migrate to major Indian cities from rural to urban areas every minute. It is envisaged that by 2050, the number of people living in Indian cities will reach 843 million. To accommodate this massive urban migration, India needs smart cities.

On the other hand, housing as an industry is still hand-crafted and depends heavily on manual labour and site construction, which lead to large amounts of material wastage and labour inefficiency. The need of the hour is to develop innovative methods to reduce construction costs without compromising quality. Hence, we must look at newer, energy efficient, environmentally friendly materials and technologies that minimise skilled inputs and deliver faster results at affordable prices.

MASS HOUSING PROCESS AND CHALLENGES

In mass housing projects concrete is the material of choice because of its multiple advantages. Concrete is used in almost all components of the structure.

Generally in mass housing projects the construction period accounts for 25-35% of the total project duration. Construction costs contribute as much as 50-60% of the sale value of the housing unit. Since, the construction cost makes up the major chunk of the sale value, it’s of prime importance that this cost is kept to a minimum. Hence, adoption of new technology and innovation are the key for successful selling of such housing units to the vast majority of the disadvantaged population.

Besides reasonable profitability, cost and time savings remain the twin objectives of the project owners, developers, contractors and ready-mix companies. Today the construction industry awaits a breakthrough solution that addresses the escalating need for speed and sustainable development.

After smartphones and smart offices, India is heading towards developing smart homes and to achieve this dream we need to adopt smart and innovative concepts and Smart Dynamic Concrete is one of them. Paving the way for such trimmings in costs is the utilization of 'SDC', compatible with mass housing construction techniques using for example aluminum and plastic shuttering. Use of these practices can reduce construction cycle times by as much 10 - 20%, reduce the cost of concrete by 10- 15% and avoid employment of a large and skilled workforce. At the same time, these practices help in delivering a quality end product.

To deliver quality products, we need to design and engineer concrete which ideally achieves the following:

• Excellent stability and pumpability to accelerate the pace of construction.

• Excellent slump retention to avoid onsite irregularities.

• High flowability for complex members and structures.

• Wide adaptability of raw materials to reduce pressure on the quality control of concrete production.

• Reproducibility and consistency to achieve fair-faced concrete.

• Higher durability specifications to extend the service life of structures.

To meet all these challenges simultaneously requires a concrete that fulfills contradicting requirements: cost-efficiency, self-compaction and robustness. This can be made possible with the utilization of Smart Dynamic Concrete (SDC).

SDC is making significant progress in addressing these challenges by providing economically and ecologically sound solutions that contribute to modern, comfortable and sustainable housing by lowering energy consumption, offering a faster construction process while increasing building life expectancy.

One of the several projects that has benefited from such a technological advancement in concrete technology is the Mass Housing Slum Clearance project in Bengaluru (formerly Bangalore). Its applications and properties have been presented in the case study below.

AN INSIGHT INTO SMART DYNAMIC CONCRETE (SDC)

Smart: innovative polymers that are based on the principle of intelligent and self- organising molecules.

Dynamic: the concrete produced is highly fluid and self-compacting.

Concrete: adds value to the overall production, placement and performance of concrete.

Polycarboxylate ether (PCE) based superplasticiser combinations provides low fines self-compacting concrete for everyday use. The superplasticisers contain an essential and unique component which is a breakthrough and revolutionary type of viscosity modifying agent (VMA). This unique concept of low fines SCC is known as Smart Dynamic Concrete.

The VMA is a synthetic co-polymer and its molecular structure and properties can be controlled directly at the synthesis stage, therefore the performance is more stable and reliable than conventional viscosity modifying agents. Conventional VMAs can provide variability in performance and hence are less forgiving and harder to control. Besides, overdosing can result in significant reduction in the workability of concrete.


Fig. 2a	Fig. 2b

SDC is based on an optimized mix design programme, incorporating products that are tailor-made to substitute the paste quantity with paste quality. This allows for a mix design which is robust and selfcompacting with low fines and thus economical and suitable for everyday concreting. These products are especially formulated to provide a unique 2-in-1 admixture solution to obtain concrete mixes withexceptional stability and fludity at the same time. Significant enhancement in engineering properties of concrete are observed using the SDC concept.

Benefits of Smart Dynamic Concrete to various stakeholders in the construction industry:

Architects & design engineers

• Enables designers to break away from traditional restrictions on building design due to complications with concrete placement.

• Can be confident that what is prescribed, translates into real life concrete.

• SCC properties achieves better finish with improved durability.

Contractors

• Accelerates and simplifies concrete placement shortening construction time.

• Less dependency on skilled labour.

• Avoids declining concrete strength development caused by retempering with water.

• Increases efficiency and longevity of equipment due to less wear and tear.

• Reduces noise and associated risks from vibrated concrete.

• Ensures construction quality.

Ready Mix Producers

• Increases the robustness of the low grade mixes subject to material variations.

• Helps achieve product differentiation and market competitiveness.

• Faster transportation, discharge, pumping and placement.

• A 2-in-1(single) admixture reduces logistical hurdles involved in handling two separate admixtures.

• Reduces cement consumption & eases shortages.

• Increased efficiency and longevity of equipment.

• Avoids declining concrete strength development caused by retempering with water.

LOW FINES CONTENT SELF-COMPACTING CONCRETE (SCC) RHEOLOGY OF SDC

Fluid concrete rheology can be defined by two main parameters that characterize its behaviour: the yield value that measures the resistance to motion from the still condition and the plastic viscosity that measures the resistance to increase the motion speed (Fig. 1).

Concrete mixes with high yield values are stiff and resist movement and those with high plastic viscosity are fluid but move very slowly. If the plastic viscosity is too low, it is very fluid but incapable of maintaining particles of cement and sand in suspension within the matrix and leads to severe segregation and bleeding. A stable concrete mix needs to have its yield value and plastic viscosity within the blue area but its behaviour does not yet comply with SCC requirements, only the green area concrete is stable and its behaviour complies with SCC requirements. The desired conditions however are obtained in standard SCC by the use of high quantities of fines, while in SDC it is obtained with a special VMA (Scheme 1).

The VMA enhances concrete stability and robustness, through the following mechanism, (described in Scheme 2): Long molecular chains link cement and fine aggregate. Through their functional groups, they act as “flexible glue” in a sort of net that maintain particles in suspension.

This mechanism allows the formation of a stable concrete paste even with less fine particles, in a very fluid system. Such a VMA is therefore capable of converting a segregating concrete mix into a stable one, making the mix robust through its unique mechanism.

BASF supports the Mass Housing segment by addressing key constraints of participants across the construction value chain. SDC technology has been applied in 22 Mass Housing projects so far, in places like Hyderabad, Delhi and in Maharashtra, Mumbai, Pune and Vapi all of which are expected to benefit over 50,000 families. One such case study of particular interest is discussed in the sections below.

Case Study: Mass Housing Project in Bengaluru

SDC at the Bengaluru Mass Housing project will help create 6,000 residences for low-income families.

Project Background

Design, build and transfer of 3,866 ground plus three floors (G+3F) dwelling units and 1200 ground floor dwelling units with comprehensive developments for the urban poor in the identified slums in the city ofBengaluru was undertaken by the Karnataka Slum Clearance Board (KSCB) in the year 2010. The project was awarded to the contractor, D.E.C Infrastructures & Projects (India) Pvt Ltd in three packages. The design consisted of a conventional framed structure of shear wall with monolithic concrete with a minimum grade of M20.

KSCB required the houses to be constructed at a faster rate since they had to demolish the existing tenements and provide shelter to the slum dwellers at temporary locations and then shift them back in to their new houses. To decrease the project tenure, D.E.C required sturdy metal forms that could be used to pour concrete for one unit and then lifted for the next unit and pour directly above. The gap between the shutters was a nominal 100 mm. This modular shuttering system also facilitated casting of walls 3 metres high together with the upper floor or roof slab depending on the structure. For a swift and efficient construction process, door frames, block outs for windows and ventilators and other required openings were provided in the formwork.

Project Challenges and Customer Requirements

• Faster construction

• M20 grade concrete with 50% strength gain in 3 days

• Minimum slump of 160mm at discharge

• Demoulding within 24 hours

• Good surface finish to avoid repair cost and plastering

• Concrete surface finish ready for painting

The RMC producer was finding it difficult to maintain stability and pumpability of concrete with regular mixes since some of the sites were far off from the batching plant. Unable to maintain the specified high workability, the contractor was ending up with honeycombs and other undesired defects. Also with delays in placing concrete there were many rejections of concrete (with conventional SNF based admixtures) loads with low slumps.

Approach and Solution

Taking into account the challenges faced by the contractor, it was suggested that SDC be considered. After discussions with the contractor and RMC producer, mockup site trials were carried out with SDC in the presence of the KSCB officials and engineering consultants.

The slump flow of concrete was maintained around 550-580 mm at the point of discharge, the mix was cohesive with no visual signs of segregation and bleeding. Due care was also taken to ensure that the shutters were leak proof and had an appropriate shuttering oil applied to achieve the right outcome. After thoroughly evaluating the performance in its plastic and hardened states, KSCB approved the use of SDC.

The RMC producer benefitted from the supply of SDC due to value-addition compared to conventional concrete. Moreover, use of the SDC admixture ensured there was no drastic drop in workability at the point of discharge. This resulted in fewer rejections of loads and retempering of concrete at site was eliminated. Once poured into the formwork, minimal or no vibration was required. With self-compacting properties, less energy and manpower were used for pumping, placing and finishing operations.

With SDC there were no honeycombing or undesirable voids, thereby achieving a good finish with low repair costs. Deshuttering happened in 16 hours which meant faster rotation of shutters and quicker completion of work. Although the concrete was highly flowable it achieved 50% strength in 3 days which reduced the cycle time. Elimination of vibration meant greater use of the formwork. Whilst usage of PCE+VMA superplasticiser (2-in-1 admixture) instead of regular superplasticisers increased the cubic metre cost of concrete for the project, the contractor achieved greater overall savings. These savings and benefits were consistently derived through the employment of less manpower, equipment, energy and repair costs without sacrificing the quality of construction and durability.

SDC provided a more environmentally friendly and sustainable solution by making it possible to adopt a special mix design using 100% manufactured sand as the fine aggregate. Taking it one step further, the binder comprised OPC with 50% GGBFS making it greener, without compromising the early and ultimate properties of concrete. The mix design is shown in Table 1.

Table 1: SDC Mix Design See Page Number 289/ 299 for the Table

Fresh concrete properties

Initial slump flow: 640-660 mm

Slump flow at site after 2 hours: 550-580 mm

Hardened concrete properties: These are shown in Table 2.

Table 2: Hardened concrete to properties See Page Number 289/ 299 for the Table

Age 3d 7d 28d

Mean Compressive

Strengths (MPa)

12 21 32

CONCLUSIONS

SDC is capable of not only meeting but also exceeding the requirements demanded by Mass Housing projects in India.

Mass Housing projects utilizing SDC technology are driven by speed and quality of construction.

Low fines SCC suits the needs of such concrete, where more than 90% of the concrete is 25 MPa and

below owing to the design and low levels of reinforcement.

SDC adds value and benefits to all the stakeholders in the construction industry by offering less

labour dependency and shorter cycle times.

SDC offers sustainable and green solutions for Mass Housing concrete.

Lastly, the authors would like to acknowledge the support and permission granted by the management of

BASF for publication of this paper.

REFERENCES

Recommendation for Self-Compacting Concrete – Japan Society of Civil Engineers, Tokyo, Japan, August 1999.

Wallevik, O.H., 'Rheology - A Scientific Approach to Develop Self-Compacting Concrete', 3^rd International Symposium on Self-Compacting Concrete, Rilem, Reykjavik, Iceland, August 2003, P. 10.