In the first of the two-part series, Upen Patel, Business Director, BASF India, explained various factors responsible for the corrosion of concrete. In this second and last part, the author explains various components and the materials used to deal with the problem of deterioration of concrete.Once concrete repairs and strengthening was considered as an activity of rejuvenating the old structures and making them capable of loadings and environmental stresses in the future life. Today we are constructing more advanced and ever more-demanding structures with complex detailing and concrete repairs and strengthening starts during the construction stage itself. The complex and fast pace construction methods with reduced emphasis on adequate quality assurance results in to construction errors and creates needs for repairs and strengthening during construction. With the complex performance demands of the new structures and ever longer life expectancies makes concrete repairs, strengthening and protection procedures more and more demanding. This article is an attempt to present the fundamentals of concrete repairs and strengthening in a step-by-step process and focuses on the advantages and disadvantages of current practices and provides an insight in the futuristic but more simple to adopt techniques.Treatments of cracks:The most important criteria for selecting the right material for crack injection is based on the structural status of the crack. Is the crack alive or dormant? This can be checked by monitoring the crack width. If the crack is live, stressed are still like to relieve and hence to avoid further cracking at any other location. It is important to inject and seal the live crack with flexible injection resin such as polyurethane based. The dormant structural cracks can be sealed with epoxy/ polyurethane resins meant for structural bonding. In case if the sealing is only meant for water tightness same can be achieved by injecting with the re-swell able acrylate injection resins. The surface cracks found within the concrete covers can be open, routed and sealed used acrylic sealers as they are superficial nature but needs effective sealing as can leads to other form of corrosion/deterioration. Many hairline cracks formed on the surface of concrete cannot be opened and sealed and can be coated and sealed with high-elongation, flexible acrylic protective coatings instead.Surface preparation for volume replacementsThe surface preparation is a pre-requisite for an effective volume replacement job. Following components explains the surface preparation tasks.??Remove all identified defective concrete??Saw cut perimeters – 15mm depth??Expose steel unit no corrosion is evident??Expose the full circumference of the steel and beyond by 25mm.??Priming of the rebars: Prime immediately after cleaning. Apply a continuous coat of active zinc rich epoxy primer or appropriate corrosion protection system. Attention must be paid to the underside of the bars.??Priming of the concrete: Depending upon the need of the volume replacement materials, apply right primer. In case of chloride contaminated area use epoxy bonding agent.Cosmetic volume replacement:While replacing the concrete volume within the cover is defined as cosmetic repairs. The aim is to replace defective, deteriorated concrete cover with impervious polymer-modified mortar. The most cost effective repair materials are ready to use re-profiling mortars or to use site-batched polymer modified repair mortars with 1:5:15 proportion of polymer: cement: sand. These mortars are not capable of achieving the high compressive strengths but are able to provide effective corrosion barrier at economical costs. As the repair is within the cover zone, it does not have significant barring on the overall strength of the structure. The ready to use re-profiling mortars are shrinkage compensated and have good thixotropy enabling up to 50mm thickness built-ups in single operations; while polymer modified site batched mortars may need multi-layer applications on thick applications.Structural volume replacements:While replacing the volume of the concrete beyond concrete cover, it is very important that the member under repair is relived from the imposed loads by supports. Surface preparation is very important and any negligence may cost the success of the structural repairs. There are many options available for volume replacement such as micro concrete, single components patch repair mortars, two-component patch repair mortars, spray applied micro-concrete, site batched polymer modified mortars, self compacting concrete, shotcrete, pre-places aggregate concrete. Large volume concrete repairs can be conducted using self-compacting concrete, shotcrete or pre-placed aggregate concrete provided the interface between new and old concrete is taken care properly. Generally in India the 1st choice for volume replacement remains as form and pour micro-concrete while spray applied micro-concrete is very popular internationally due to reduced need for shuttering and ready availability of spray applied micro-concretes. Patch repair mortars if need to be used must be ready to use, one component type with fibre modification to avoid chances of cracking. Products like two-component polymer modified mortars and site-batched polymer modified mortars known for their low compressive strengths and can not be used to repair high grade concrete. In most parts of India, it’s not practical to produce site-batched polymer modified mortars with >M20 grade compressive strengths due to limitation of local fine aggregate gradation! If such low strength mortars are used to replace concrete, it leads to higher stress concentration on the rest of the structure resulting in to further distress and deterioration.Special application:Application such as under water, chemical exposures, pavement repairs, and abrasion/impact damage as well as heritage restorations requires additional considerations while repairs and now many specialized products are available for such applications some of them are summarized as below:Underwater repairs??Micro-concrete: Emaco S46UW – Anti-washout grout??Patch repair mortar: Emaco S90 – Thixotropic patching mortar??Crack injection resins: Concresive 1316 – Water insensitive resin??Re-profilinfsealing mortar – Subcote S – Resin basedChemical resistance situation??Epoxy concrete – Concresive 2929??Patch repair mortar – Concresive ERL – Epoxy liner??Re-profiling / sealing mortar – Concresive 2200 – Resin basedPavement repairs??Patch repair mortar – Emaco R650 – Rapid hardening cementitious??Re-profiling mortar – Concresive 1418T- Rapid hardening, resinousCorrosion controlWhile repairing the deteriorated structure it’s of utmost importance to prevent the rest of sound structure from getting deteriorated by implementing proper corrosion control measures. There are various options available the right selection needs to be based on the need of the situation and the practically of the options. Following is the basic introduction with the advantages and disadvantages of some of the most popular option:Film forming coatings – Acrylics and resin based coatings??Limited life expectancy (5-10 years)??Limited crack bridging limits performance on cracked substrate??No passivation of corroding reinforcementMigrated corrosion inhibitors – surface applied method??Easy to use??Effectiveness depends on chemical types and concrete porosity??Not effective against carbonation, sulphates, ASRCathodic protection – impress current method??Good life expectancy (>20 years)??Very expensive??Destructive, slow and time consuming??High application skills required??Power breakdown can disrupt the protection??No protection against carbonation, sulphate, ASR attacksCathodic protection – Impress current method??Low to medium life expectancy (5 – 10 years)??Destructive method, requires replacements in future??Lump-sum application, design guidelines not followed??Not practical in heavy reinforced members??Corrosion continues; instead of steel embedded zinc corrodes??Not effective against carbonation, sulphates, ASR.Protectosil CIT – Organo-functional silane based system??Spray applied – easy to use??Organo functional silane based – deep penetrative??Monomer structure – chemically reacts, no degradation in UV??Corrosion inhibition effect – repassivates rebar??Effective in all four types of corrosion as it hydrophobize concrete??Well-established and tested worldwide??Non destructive method??Measurable reduction of corrosion current??Effective till treated concrete thickness lasts!Other important aspects of repairsWhile right diagnosis and selection of materials is the core of the repair project; other aspects such as preparation of drawings and specifications, selection of right contractor, execution of the work to the specifications, adequate quality control are equally important. Repair project is more specialised and good site management and construction practices have to be followed. Also at the end of the job all the records relating to the diagnosis, material selection and execution of the work shall be maintained and preserved for any reference needs in future.Conclusion:With the right focus on the causes, evaluation and selection of correct repair materials; the resultant repairs would be long lasting and we would be able to avoid expensive repetitions of repairs in the future.(Extract from the paper presented by the author at the Construction Chemicals International Conference 2012 held in Mumbai)
Adani Group eyes Jaiprakash Associates’ Shahabad cement plant
Adani group has reportedly expressed interest in acquiring a cement plant from Jaiprakash Associates, located in Karnataka with a capacity of 1.2Mt per year. The plant is reportedly in the middle of an as yet incomplete deal between Jaiprakash Associates’ and Dalmia Bharath for a value of US$671mn for a transfer of the former’s cement and power plants.
It has also been reported that Adani Group is in talks with several companies over possible acquisitions as a means to double its cement producing capacity to 140mt per year by the end of 2028.
Dalmia Bharat records a hike in cement sales
Dalmia Bharat recorded a rise of 9.6 per cent in its sales y-o-yfrom 12Mt in the first half of financial year 2023 to 13.2Mt in the first half of financial year 2024. This rise has led to an increase in earnings from US$116m to US$144m during the same period. The company started commercial production from their new 5,00,000t/yr capacity clinker plant in Ariyalur and 2mt/yr Sattur grinding plant, both located in Tamil Nadu, raising the company’s clinker capacity to 22.2Mt/yr. This increase in capacity was attributed largely to the company’s foresight in estimating high growth in construction material demand in the country due to a boom in infrastructure development. The company has also managed to reduce their carbon footprint to 456kg/t of cement, lowest recording globally in the cement industry.
Total cost of decarbonising Indian cement and steel industry estimated at USD 627 bn
The Council on Energy, Environment and Water (CEEW), funded by power provider BP recently reported that it will require a Capital expenditure investment of USD627Bn to decarbonise the Indian cement and steel sector, to reach net zero CO2 emissions. According to the report, the Waste Heat Recovery (WHR) and other similar efficiency enhancing upgrades to cement plants can help reduce the industry’s emissions down by 32 per cent immediately.