There is a need for technologically advanced concrete admixtures for the ready-mix industry that meet industry codes and meet or exceed the demands of challenging construction applications and adverse placement conditions. Advancements in concrete admixtures address the Urban Concrete needs such as Workability Retention, Precast Application, Enhancement in Concrete Rheology, and Variations in Concrete Strength.

Urban Concrete: Requisites & Remedies

Shivram B Bagade, General Manager - Singapore and Brunei, and Regional Business Development Manager BASF South East Asia Pte. Ltd, Singapore

The swift shift in the dynamics of concrete during recent years have posed a lot of challenges for concrete technologists and concrete professionals across the globe. In the process of making modern concrete, one needs to pay greater attention not only to aspects such as the mix design but also to its performance with respect to handling, pumping, placing, finishing, and curing. Durability and sustainability are the buzz words now. Hence, its essential to have a better know-how on concrete making materials, such that one can extract the best potential from these ingredients.

Emerging trends in construction and construction practices demand a holistic approach by various stake holders of the construction industry for successfully specifying and making Urban Concrete. Alternative aggregates, requisites and remedies to make urban concrete, poor rheology, stickiness, workability retention, pumpability and placement of modern concrete are some of the major pain points, which need immediate attention. Advancements in concrete technology because of newly developed materials such as chemical admixtures have assisted in improving the properties of concrete and address most of the above-mentioned pain points.

Infrastructure is one of the important elements of economy. It comprises the basic framework, facilities, networks (Water, Sewerage, Transport, Power, Communications) and buildings that must function efficiently and improve the people’s standard of living. There are enormous renovation needs in developed countries, while in emerging markets, infrastructure and urbanization are essential for reaching their expansion goals. Another reason for a surge in infrastructure spending (encouraging urbanization) is the political will to boost economic prospects in as many regions as possible.

It’s time now for construction professionals to align with emerging technologies and make use of advancements in building materials, construction equipment and construction methods to address the needs of affordable housing, well-functioning infrastructure for water, traffic, energy, sanitary and waste treatment, environmental protection, Smart cities, Green Cities, efficient mode of transport, and so on. Due to the high demand for infrastructure, the construction industry needs more resources such as manpower, material and machineries. In such a scenario, resource efficiency is and will be a challenge for the construction fraternity.

Infrastructure Challenges For Ready Mix Industry
The ready-mix business is a diverse and demanding sector with its own requirements and challenges despite several technological advancements in the field of ready mix. Ready-mix operations are always local, with key factors such as financial resources and transportation playing a central role in decision making. Challenges include Operational challenges; Supply Chain challenges, and Technical challenges.

Strength, durability and place-ability are at the forefront of challenges faced by ready mixed concrete producers as well as the need for concrete that is aesthetically pleasing, more sustainable, and safer to use. Hence, there is a need for technologically advanced concrete admixtures for the ready-mix industry that meet industry codes and meet or exceed the demands of challenging construction applications and adverse placement conditions.

One of the wishes from the wish list of ready-mix producers is to have the right Admixture partner with broad-based product solutions which can provide added value to increase the service life of concrete, enable speed of construction, bring environmental efficiency and liquid colouring products for aesthetically pleasing architectural concrete.

Innovative Admixtures & Technolgies
Today, in the field of Concrete Technology, there is a revolutionary shift; any properties of Concrete (Green or Grey) can be achieved without difficulty. This has been aided due to the developments in the field of Construction Chemicals, especially in Admixtures. To quote Mr. V.M. Malhotra who 37 years ago had said: “There have been very few major developments in concrete technology in recent years. The concept of air entrainment in the 1940s was one; it revolutionized concrete technology in North America. It is believed that the development of super-plasticizers is another major breakthrough which will have a significant effect on the production and use of concrete in years to come.” This has been proven correct.

Ready-mix concrete is characterized by a great number and variety of different mix designs. Utilizing different types of fillers, cements, and binders together with the increasing requirement for better performance and durability-based concrete specifications. At the same time, ready-mix producers must maintain their profitability in the face of rising materials, labour and equipment costs. As a result, producers are optimising their production and logistic costs. The innovative admixture systems from Master Builders Solutions of BASF, support these goals by providing the capability of delivering high-quality concrete at any time to the jobsite. This new concept facilitates the production of concrete with both extended workability and a low water/cement ratio. Cost savings in production may be realized through mix design optimizations for cement types and aggregate composition. As a result, these technologies enable ready-mix producers to optimize inventory, facilitate logistics, and reduce investments in tanks and dispenser equipment and thus also decrease maintenance costs.
Table 1: Urban Concrete challenges addressed using innovative admixture
Process Step Admixture Solutions for:
Materials
  1. Higher Usage of Manufactured Sand
  2. More Sustainable Concrete Mixtures
Mixing
  1. Faster Mixing Times
  2. Production of Ultra High Strength
Transit
  1. Improved Slump Retention
Placing
  1. Reduction of Concrete Stickiness
  2. Easier & Faster Placement of Concrete
Hardening
  1. Faster Early Strength Development
Hardened Properties
  1. Reduction in Shrinkage and Cracking
  2. Replacement of Steel Reinforcing

Building blocks used in PCE TechnologyFigures: Building blocks used in PCE Technology

Admixture tailored for extended workability retention
As shown in Figure 1c), SuperPlasticiser-Super Retaining Polymer (SP-SRP) contains a large amount of building block A, responsible for workability retention. Hence, the composition should qualify this admixture for RMC application where long transportation times are typically encountered, under severe conditions like hot weather or difficult aggregate or cement conditions. We decided to apply SP-SRP in a 30 MPa strength class concrete, where the designed slump upon delivery to site is 10-14 cm.

In this case, SP-SRP enables the RMC station to adjust initial slump at the batching station to the designed slump at delivery. The perfectly flat performance of SP-SRP ensures that, no matter when the concrete arrives at the site (as long as it is within 2 hours), the specification is matched. Retarded Naphthalene based, however, cannot be treated that way. Due to the severe slump loss, the batching plant would have to adjust to a slump higher than the specification requires, with consequences for the mix proportion. Furthermore, due to the slope of the slump loss curve, the actual slump delivered on site is dependent on the actual transportation time, which makes it challenging to hit a tight specification like in the example given, and re-tempering at the jobsite eventually has to occur.

Admixture tailored for precast applications
Super Plasticiser-High Early Strength (SP-HES) molecules are rapidly adsorbed on the surface of the cement grains and act through electrostatic and steric repulsion to powerfully disperse the individual particles of cement.

The molecular structure of polycarboxylate ether polymers is essential for the early development of strength. With conventional PCE superplasticisers, the molecules cover the entire surface of the cement grain and build a barrier against contact with water. Therefore, the hydration process takes place slowly.

The unique, proprietary molecular structure of SP-HES exposes increased surface of the cement grains to react with water. As a result of this effect, it is possible to obtain earlier development of the heat of hydration, faster development of the hydration products and, as a consequence, higher strengths at very early age. This advantage can even be utilized at low temperatures.

The unique mechanism of this new polymer technology allows it to be adsorbed into the cement without inhibiting the hydration of the cement. Thanks to this technology, SP-HES exhibits 10-20% higher early strength development than traditional technology while providing good slump retention.

The composition of SP-HES indicates that the performance would be useful in precast applications, where workability retention requirement is often only for less than 1 hour, due to batching plant being in the proximity of the precast yard. In fact, SP-HES provided sufficient slump retention in the actual application under hot climate conditions. Applying SP-HES in a high slump concrete, leads to a slump loss not greater than 4 cm after one hour, even at 35ºC ambient temperature. The slump retention of conventional PCE admixture, on the contrary, is only acceptable for approximately 20 minutes.

With the slump life extended, one would anticipate early strength is inferior in case of SP-HES. However, SP-HES shows not only equal early strength compared with conventional PCE, but after 28 days at standard curing conditions the strength exceeds the benchmark by 12%.

It is noteworthy, that due to the chemical nature of the mechanism of the new admixtures, its effect is quite dependent on the cement composition. Apparently, even though the early strength development can differ significantly, it is always improved, and differences are leveled out at later ages, where a strength increase of up to 15% can be expected, compared to conventional PCE admixture. The mechanism behind the difference in strength development, which is dependent upon the cement composition, is currently under investigation and remains unclear at this point of time.

Admixture tailored for Concrete Rheology enhancement
In case of Urban concrete, given the expected service life of structures, authorities and consultants specifies stringent durability requirement. In the process of making urban concrete, one needs to pay greater attention not only to aspects such as the mix design but also to its performance with respect to handling, pumping, placing, finishing and curing. Durability and sustainability are the buzz words in modern concrete world. Durability is at fore front in making urban concrete.

To achieve the desired durability requirements, concrete technologists must make use of higher amount of supplementary cementitious materials, ingredients like micro silica becomes an essential, lower water content in concrete mixes is mandatory. Such concretes with lower water and higher powder creates enormous challenges in batching and mixing of concrete. Longer mixing times reduces the operational efficiency and the concrete stickiness will be a major issue during pumping, placing and finishing of concrete.

The concrete technologist has limited options to reduce the stickiness of mixes given the lower water binder ratio and higher binder contents which are essential to achieve the desired durability parameters. This creates a demand for a solution to minimize the stickiness and hence concrete Rheology is one of the important parameters when it comes to making urban concrete. An advancement in polymer science and the innovation know-how, scientists have developed a new generation of polymers bringing a significant improvement in the rheological properties of concrete.

Urban concrete mixes often demonstrate a higher viscosity due to their low water contents. Although having a high level of workability, the concrete often appears harsh, sticky and therefore difficult to pump and process. This is especially true for engineering concrete with low water/cement ratios optimized towards having a low environmental impact. To overcome these challenges BASF has developed MasterEase, a new admixture range developed for low-viscosity concrete, With the new technology, plastic viscosity can be reduced by up to 30%, which results in a substantial reduction of pumping pressure required to pump the concrete on the construction site.

Placing and finishing of the concrete is much easier, faster and hence more economic than using standard concrete. Ease stands for easiness of mixing, pumping, placing, leveling and finishing of concrete. Flexible and adaptable with improved workability retention Concrete producers and users benefit in many ways from the new technology. It is flexible and can be adapted to challenging situations such as temperature variations. Moreover, the high level of rheology and workability retention minimizes the risk of jobsite addition of water. This is a real added value for the contractors in terms of concrete durability. The concrete is easy to place, trowel and pump.

Utilizing this concrete save time and cost in every single construction project, it improves the utilization of the transportation fleet and equipment and reduces the wear of mixers, pumps and pipelines. In addition, the possibility to reduce mixing water even further without impacting the concrete rheology, opens new possibilities for improvement in concrete mix designs. Less water in concrete mixes implies higher performance and better durability. The new technology is particularly suitable for concrete mixes which are optimized for advanced engineering properties and sustainability. High strength concrete with low water/cement ratios, as well as mixes with higher levels of secondary cementitious materials, reduce the CO2 footprint and are easier to produce and place. This helps engineers and investors to improve sustainability ratings of their projects.

Admixture tailored for Concrete Strength Enhancement
Given the fluctuations in concrete making materials and the concreting practices, achieving desired Concrete strength in modern days is a new challenge. Inferior Concrete workability at time of placing encourages the workforce for addition of water, which in turn reduces the concrete strength. Inconsistency in concrete making ingredients and variations from batch to batch of materials is a major pain point for Concrete professionals. The necessity of switching to alternative ingredients such as natural/river sand to crushed rock fines/manufactured sand impacts a lot on concrete strength, if appropriate changes in concrete mix design are not adopted.

Urban concrete and its durability requirements will demand higher replacement of Supplementary cementitious material. Not only the higher replacement of Supplementary cementitious material but also to accommodate the inconsistency of these materials, concrete professionals needs a whole new approach of mix design to achieve the desired strength of concrete. Hence a robust solution to address the concrete strength issues is need of the hour.

With the advancement in chemistry and concrete admixture science, BASF Mater Builder solutions have developed, a revolutionary technology that redefines concrete strength and durability. It allows concrete producers to expand concrete performance while reducing the environmental impact. Master X-Seed STE is an innovative strength-enhancing admixture solution for the construction industry, which significantly improves both early and late-age strength development in concrete. The new solution, Master X-Seed STE, also helps make production of concrete more efficient.

The concept originated from BASF’s X-Seed, a unique seeding technology used to promote cement hydration and speed up concrete hardening. Master X-Seed STE further enhances concrete’s strength development and performance characteristics. Specially formulated for Asia Pacific concrete market, Master X-Seed STE admixture utilizes calcium silicate hydrate (CSH) nanoparticles, along with other technologies (admixture solutions), to facilitate and improve strength development at all ages of the concrete. Master X-Seed STE enables the increased use of supplementary cementitious materials, thus helping to reduce carbon footprint associated with concrete production. Master X-Seed STE admixture allows concrete producers to expand the performance space of a given concrete mixture and optimize the cementitious content, by permitting a strength safety factor up to 15%. This allows earlier stripping of forms to improve production efficiency. It is recommended for use in ready-mixed and precast concrete and Self-Consolidating Concrete (SCC).

Concluding Remarks
While we build more and more urban cities to accommodate the needs of future urbanization, concrete and its importance as a building material cannot be denied. In fact, the innovative use of concrete can only add to its importance in coming times. For Infrastructure business to increase its commercial viability and its relevance, contractors and builders need to look beyond the traditional boundaries defined by existing construction practices, market segments and the built structures. A holistic approach by all the stakeholders in the construction industry is required to address the urban construction and concrete challenges.

New and rapid developments in nano chemistry can certainly aid in the progress of concrete technology. This, in turn, can make the construction processes more efficient, faster and economical. Admixtures have the potential to minimize costs related to wastage and energy usage. More importantly, these factors contribute towards achieving good construction practices with lower carbon footprints.

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. Modern architecture, large scale and high-rise constructions demand building materials that provide durability and energy efficiency. The innovative admixture technology will be the driving force for the development and growth of infrastructure. The Master Builder solutions from BASF meet most of the challenges and requirements.

The construction industry professionals need to look at newer, more energy efficient, environmentally friendly materials and technologies that minimize skilled inputs and deliver faster results at affordable prices.

References
  1. Recommendation for Self-Compacting Concrete – Japan Society of Civil Engineers, Tokyo,Japan, August 1999.
  2. Women in construction. Editor K.N. Vaid, National Institute of Construction Management and Research, Walchand Centre, Tardeo, Mumbai 400 034. 1999 Cement Statistics 1999, Cement Manufacturing Association, New Delhi 1999
  3. Dewar, J.D. and Anderson, R. Manual of Ready-Mixed concrete, Blackie Academic and Professional. UK. 1992.
  4. Ready Mixed Concrete - its key role in European construction. European Ready Mixed Concrete organization, PO Box 19, Egham, surrey TW20 BUT, UK. 1997
  5. Gaynor, R.D. Ready mixed concrete, ASTM STP-169, American Society for Testing and Materials, USA
  6. Takeyama. M. Present technology of ready mixed concrete and future prospects. Magazine of concrete Research, September 1996. Vol. 48 no. 176 pp. 199-209
  7. Verma, C.L. Jain, S.K. and Rehsi. S. S. Techno-economic feasibility study for the production of ready-mixed concrete in India. The Indian Concrete Journal, October 1978 Vol-54, No. 10, pp 257-259
  8. Development of readymix concrete to be transported without agitation. Unpublished report, project TG-204.Cement Research Institute ofIndia, June 1979
  9. Ready-Mixed Concrete growth prospects in India A K Jain*, Grasim Industries Ltd, India
    27th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 29 - 30 August 2002, Singapore
  10. THE INDIAN EXPERIENCE OF READY MIXED CONCRETE (RMC) C. R. Alimchandani, STUP Consultants Ltd., India 32ndConference on OUR WORLD IN CONCRETE & STRUCTURES: 28 - 29 August 2007,Singapore
  11. Corradi M., Khurana R. Y, Magarotto R.; Controlling Performance in Ready Mix Concrete, Concrete International Vol. 26, No. 8, 2004, 123-128.
  12. Concrete Admixture Handbook V.S. Ramachandran.
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