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Changing normal concrete into durable concrete for tunnelling application

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In this second part of the two-part series paper, the author EugenKleen of Mc-Bauchemie Mueller GmbH and Co.KG looks at the materials required to change normal concrete to durable media resistant concrete for use in tunnelling application.The main materials, which can help change normal concrete to durable aggressive media resistant concrete, are:??New generation PCE based admixtures??Condensed silica fume or microsilica slurry or??Latest generation aluminosilicatePCE based admixturesMost of the new generation superplasticizers are from the Acrylic Polymer (AP) family. Polycarboxylate is a common term for the substances that are specifically used as Polyacrylate or Polycarboxylate ether (PCE). The PCE based Super Plasticizers are by far superior to the conventional once with respect to initial slumping as well as slump retention with time. The efficient working of these plasticizers is due to the new type of molecule designs. PCE based superplasticizers produce excellent properties when used with cementitious materials. The disadvantages associated with longer setting times of conventional superplasticizers is offset by PCE based super plasticizer and therefore its use in concrete can also attain high early strengths. The development of highly effective superplasticizers with long and consistent duration of action is therefore an important precondition for the production durable concrete, due to low water contents and high early strength requirements.Concrete additives based on PCE offer advantages like:Significant reduction of the water demand of the mix??Little loss of consistency??Short setting times??High early strengths??Low tendency to segregationThe advantages of these new generation polymers are very clear, not only in terms of performance but also in terms of the dosages used for similar conditions and this factor balances the disadvantages in economy, as new generation superplasticizers are relatively expensive per unit price.Condensed Silica Fume/Microsilica:The term ‘microsilica’ is adopted to characterise the silica fume, which is used for the production of concrete. Microsilica or Condensed Silica Fume (CSF) is a by-product resulting from reduction of high purity quartz with coal in the electric arc furnaces used in manufacture of silicon, ferrosilicon and other alloys of silicon.There are three main reasons for the incorporation of silica fume as an additive for HPC. Microsilica has a filter effect i.e. very fine particle distributed itself in the space between the materials in the concrete in a homogenous way to give rise to more dense concrete. Silica fume improves the strength of the transition zone between cement paste and aggregates. CSF is highly pozzolanic in combination with Portland cement.During cement hydration there is surplus of calcium hydroxide. The added condensed silica fume’s SiO2 reacts with surplus of calcium hydroxide, which are greater amounts of calcium silicate hydrate, which are denser and stronger than calcium hydroxide. The pozzolanic reaction and the filler-effect lead to a compaction of the cement paste and the conversion of CH crystals into CSH gel leads to homogenous paste. The phenomenon of dense packing in the interface zone of aggregates also contributes to increase the strength of the concrete on account of aggregates fully contributing their strength of concrete with silica fume is greater than those of the matrix, indicating the contribution of the aggregate of microsilica (50:50 with water) have all the benefits in transportation, dispensing methods, mixing times and dispersions to get the desired effect in durable concrete for tunnelling segments.New Generation Aluminosilicates:New generation aluminosilicates based on special nano-crystalizers have been developed. These new materials improve the properties that are crucial for the durability of high performance concrete. In addition to reducing chloride migration, an exceptional chemical and resistance to aggressive media of the concrete can be achieved with aluminosilicates. The concrete structure is simultaneously reinforced right down to nanoscale, density is improved and compressive and flexure strength as well as abrasion resistance of the high-performance concrete is increased. There is also a significant reduction of micro-crack formation, which makes it particularly suitable for the production of tunnelling concrete. Aluminosilicate reduce the proportion of portlandite by way of a pozzolanic reaction that changes it into the aluminosilicate crystals into calcium silicate hydrate. In addition to the unique resistance against acids a crystalline micro-reinforcement within the concrete structure is achieved. This reduces the risk of micro-crack formation, rendering concrete impermeable.Due to high homogeneity and reduced tackiness compared with microsilica based concrete, workability is improved significantly. In many instances this enables the production of high-performance concrete that can be pumped. In addition, a distinct improvement of the building structure’s aesthetics is gained due to the fair appearance of the concrete surface. Aluminosilicates perform over some of the disadvantages of microsilica:??Graded for dispersion in concrete??Graded particle size??Optimises mixing time within concrete??Good dispersion reduces unreacted material in the mix and increases passivation by C-S-H gel on aggregate surface??Material if agglomerated improve strength of the mix??Reduces risk of alkali silica reaction by agglomeration of aluminosilicate particles.All in all, the use of PCE admixtures and microsilica or aluminosilicate slurries in addition to the standard ingredients in concrete, plus excellent mix-design practices can facilitate the production of high performance concretes resistant to aggressive media, suitable for use in tunnelling applications.

Key difference between Microsilica and Aluminosilica


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false

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Microsilica

Aluminosilica

1

By-product of
ferrosilicium and silicium production, not specifically produced for concrete

1

Manufactured product. It
is only produced for use as concrete additive

2

Quantities are depending
on the metal industry and the economic development

2

Quantities are not
depending on other industries and are unlimited, therefore reliable
availability

3

Quality of the product
has a higher deviation because it is only a by-product

3

High quality standards
for end product because every step in production is controlled




























































































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Concrete

JSW Cement Begins Production At Nagaur Plant In North India

New greenfield integrated plant raises grinding capacity to 24.1 MTPA

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JSW Cement, part of the JSW Group, has begun production at a greenfield integrated cement plant in Nagaur, Rajasthan, marking its first such facility in north India. The company said this move raises its total cement grinding capacity to 24.1 million tonnes per annum (MTPA) and its clinker manufacturing capacity, including the joint venture, to nine point seven four MTPA. JSW Cement is described as one of India’s leading green cement producers and is positioned to expand its national presence.

The Nagaur integrated plant is equipped with a three point three zero MTPA clinkerisation unit and a two point five zero MTPA cement grinding unit, with an additional one point zero zero MTPA grinding unit under construction. The facility has been positioned to serve the high-growth markets of Rajasthan, Haryana, Punjab and the National Capital Region. The plant is intended to support construction and infrastructure demand across these nearby states.

The Nagaur unit was funded through a strategic mix of equity and long-term debt, with 8,000 mn from the fresh issue proceeds of the initial public offering (IPO) allocated specifically towards part-financing of the unit. Company executives indicated that the project was completed within 21 months and that the expansion advances the company towards its mid-term capacity target of 41.85 MTPA and its long-term vision of 60 MTPA. The commissioning was cited as an example of the company’s project execution capabilities.

The plant has been designed as a model of sustainable manufacturing and includes provisions for the co-processing of alternative fuels in the kiln to reduce fossil fuel use. The site features a seven km long overland belt conveyor to transport limestone from the mines, reducing road transport, and will soon include a 16 megawatt (MW) Waste Heat Recovery System to capture and reuse process heat, significantly lowering its carbon footprint. These measures are intended to reduce the environmental impact of transport and to lower the carbon intensity of cement production.

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Concrete

JSW Cement Starts Production At Nagaur Plant In North India

Greenfield integrated plant expands northern footprint

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JSW Cement, one of India’s green cement producers, has commenced production at a greenfield integrated plant in Nagaur, Rajasthan, marking the company’s first such facility in north India. The commissioning expands the company’s national footprint and takes total cement grinding capacity to 24.1 mn t per annum and total clinker manufacturing capacity, including a joint venture component, to nine point seven four mn t per annum. The move positions the firm to serve high-growth markets across the region. Management said the project is a strategic step towards a pan-India presence.

The Nagaur plant is equipped with a three point three mn t clinkerisation unit and a two point five mn t cement grinding unit, with an additional one mn t cement grinding unit under construction. The facility is strategically located to cater to demand in Rajasthan, Haryana, Punjab and the National Capital Region. An overland belt conveyor will move limestone and reduce reliance on road transport. Project execution was completed within 21 months, underlining the firm’s construction capabilities.

The investment for the Nagaur unit was financed through a mix of equity and long-term debt and the company allocated Rs eight bn from fresh issue proceeds of its IPO towards part financing of the project. The expansion advances progress towards a mid-term capacity target of 41.85 mn t and a long-term vision of reaching 60 mn t capacity. The commencement of operations in the north is expected to support infrastructure growth and provide customers with high-quality, eco-friendly cement while maintaining sustainability credentials.

The plant has sustainability features including provisions for co-processing of alternative fuels in the kiln and a seven km overland belt conveyor to cut the environmental impact of road transport. The facility will include a 16 MW Waste Heat Recovery System to capture and reuse heat from production and reduce carbon emissions. The operation supports the company’s ambition to be among the world’s most sustainable cement producers.

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Concrete

JSW Cement Forays Into North India With Nagaur Plant

Nagaur plant raises grinding capacity to 24.1 million tonnes per annum

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JSW Cement has commenced production at a greenfield integrated cement plant in Nagaur, Rajasthan, marking its first integrated facility in north India and extending the JSW Group’s national presence. The Nagaur unit will serve high-growth markets in Rajasthan, Haryana, Punjab and the National Capital Region. The company presented the commissioning as a key step in its pan-India expansion.

The commencement increases the company’s total cement grinding capacity to 24.1 million tonnes per annum (mn tpa) and brings total clinker manufacturing capacity, including the capacity at its joint venture JSW Cement FZC, to nine point seven four million tonnes per annum (mn tpa). The firm described these additions as strengthening its supply chain and regional reach. The Nagaur site is positioned strategically to reduce logistics for northern markets.

The Nagaur integrated plant comprises a three point three mn tpa clinkerisation unit and a two point five mn tpa cement grinding unit, with an additional one mn tpa grinding unit under construction. The facility was completed within 21 months, demonstrating the company’s project execution capabilities. Management indicated the combined configuration will improve service levels and product availability across target states.

The plant was funded through a mix of equity and long-term debt and the company allocated eight billion (bn) Rs from the fresh issue proceeds of its initial public offering to part-finance the unit. The financing was presented as part of a broader capital plan to support capacity additions and operational enhancements. The firm said the investment aligns with its mid-term growth objectives.

The site is designed with sustainability measures including provision for co-processing alternative fuels, a seven kilometre overland belt conveyor to move limestone from nearby mines and a forthcoming 16 megawatt (MW) Waste Heat Recovery System to recycle process heat and lower emissions. The company reported the expansion brings it closer to its mid-term capacity target of 41.85 mn tpa and to a longer term ambition of 60 mn tpa.

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