Alkali-Aggregate Reaction in Concrete Structures & Preventive Measures

When the alkali of cement reacts with the reactive constituents of aggregates, the reaction is deleterious though very slow, and the distress is exhibited when the volume inside the concrete is increased due to the formation of alkali-silica gel, causing the concrete to expand and crack.
Dr S.C.Maiti, (Ex) Joint Director, National Council for Cement and Building Materials

Distress due to alkali-aggregate reaction have been noticed in some of our hydro-electric projects. Bridge piers and concrete pavement have also suffered distress due to alkali-aggregate reaction in Poland and U.S.A. OPC containing less than 0.6% alkali (as Na2O equivalent) is considered to be low-alkali cement, as such cement, if used in concrete, the deleterious alkali-aggregate reaction is not likely to occur. PSC with more than 50% slag and having maximum 0.9% alkali is also considered as “low alkali“ cement. Higher slag content (say, 56 to 70%) in PSC, is permitted by IS455. But, such cement will have higher alkali content, and may be suitable against chlorides and sulphates in soil and ground water, but may not be suitable for use in hydro-electric projects, to combat the deleterious alkali-aggregate reaction.

Every cubic meter of aggregate cannot be tested. Therefore, precautions should be taken in construction e.g in hydro-electric projects’ structures, in sea, coastal areas, marshy land etc, where reactive aggregates may be there and moisture is always available for the reaction to take place inside concrete, to use PSC with 50-55% slag and having maximum alkali content of 0.9%(as Na2O equivalent). The International Commission on large dams, ICOLD does not recommend PPC in concrete, to combat the deleterious alkali-aggregate reaction, because of its variable properties.

Concrete structures  are supposed to provide satisfactory service during

Introduction
Concrete structures are supposed to provide satisfactory service during their service life. But, sometimes, they suffer distress due to chemical reactions inside the concrete. One such reaction is alkali-aggregate reaction. The alkali of cement reacts with reactive constituents of aggregates. This reaction is deleterious ,but is very slow, and after 15 or 20 years, the distress is exhibited, as the volume inside the concrete is increased due to the formation of alkali-silica gel. The gel imbibes moisture and the volume is increased. The concrete expands and cracks. Fig.1 shows a microscopic photograph of the alkali-silica gel in concrete.

Alkalies of Cement
Concrete structures  are supposed to provide satisfactory service during
The alkalies (Na2O and K2O) of OPC vary from plant to plant, as they are dependent on the raw materials used for the manufacture of cement. In case of PPC, the alkali content will depend on the alkali content of OPC, the alkali content of flyash and the percentage of flyash used to produce PPC. In case of PSC, the alkali content will depend on the alkali content of OPC, the alkali content of ground granulated blast furnace slag (g.g.b.s), and the percentage of g.g.b.s used to produce PSC. Thus, the alkali content of cements will vary from plant to plant. Typical alkali content of cements is shown in Table 1. Alkalies of cements are minor components, but they play a very important role for durability of concrete, especially when some of the constituents of aggregates are reactive.

Distress Noticed in Concrete Structures
Two of our dams suffered such distress in concrete. The Rihand dam in U.P and the Hirakud dam in Odissa. The power house of Rihand dam could not be operated for a number of years. Severe cracks were observed in the R.C.C columns. The distress noticed in the power house of the Rihand dam: (I) Cracks were observed in machine foundations in 1972. The depth of cracks in various locations are 7-45cm.(ii) There were operation problems including frequent tripping of generating units,(iii) One of the columns of the penstock gallery opened up at the cracks, and showed 9 of 10 reinforcement bars snapped at the end of the welded joints. Although about 15% flyash was used in concrete, this was not sufficient to combat the deleterious alkali-silica reaction, as the alkali content of OPC was very high(1.2%)[1].

The bridge piers suffered distress due to alkali-silica reaction in Poland (Fig.2)[2]. In U.S.A Portland Cement Association identified cracks in concrete roads due to alkali-silica reaction (Fig.3) [3]. In Korea also, concrete pavement cracked due to alkali- silica reaction[4].

Concrete structures  are supposed to provide satisfactory service duringFigure 2: Flyover Pier (in Poland) with ASR Symptoms

Low Alkali Cement
Various Standards (IS456 and International Standards) define low alkali OPC as having alkali less than 0.6% as Na2O equivalent (i.e Na2O +0.658K2O). The Bulletin No.79 of ICOLD [5] states “Portland cements containing less than 0.6% equivalent sodium oxide are considered to be low alkali cements. North American experience has indicated that deleterious expansion from alkali-aggregate reaction is not likely to occur as long as the alkali content of Portland cement does not exceed the equivalent of 0.6% Na2O”. The reason for considering PSC having higher alkali content (i.e higher than 0.6%) to be “low alkali” cement , as the alkali of slag is not fully reactive.

BS 5328:Part4[6] while describing “Methods of Test for Alkali” for blended cements, stipulates that, “For g.g.b.s, the reactive alkali shall be taken as 50% of the measured value, and for pfa (i.e flyash), the reactive alkali shall be taken as 17% of the measured value”.

For the blend of OPC and at least 50%g.g.b.s, the British Research Establishment Digest 330[7] states “When using a blend, the controlling factor seems to be the greatly reduced ability of hydroxyl ions to diffuse within the cement paste, rather than the alkalies contributed by the cement or slag. These g.g.b.s blends can therefore be regarded as equivalent to low alkali Portland cements. In the recommendations of the German Committeefor reinforced Concrete issued by DIN, a blend of 50% or more g.g.b.s with OPC or a low alkali (less than 0.6% equivalent Na2O) Portland cement are the alternatives for use with a reactive aggregate”.

Recommendations of the Indian Standards on the Alkali Limit of PSC and PPC
Regarding alkali content of PSC or PPC the Indian Standards IS 455[8] and IS1489 (Part1)[9] stipulate, alkali aggregate reactions have been noticed in aggregates in some parts of the region. On large and important jobs where the concrete is likely to be exposed to humid atmosphere or wetting action, it is advisable that the aggregate be tested for alkali aggregate reaction. In the case of reactive aggregates, the use of cement with alkali content below 0.6% expressed as sodium oxide (Na2O +0.658K2O) is recommended. However, in the case of cement having a minimum slag content of 50% (a minimum flyash content of 30% in case of PPC),a maximum alkali content of 0.9%, expressed as sodium oxide(Na2O+0.658K2O) is recommended”.

Combating Alkali-Silica Reaction in Concrete using Portland Slag Cement
Concrete structures  are supposed to provide satisfactory service duringFigure 3: Cracks on concrete pavement in U.S.A due to alkali-silica reaction
The Portland slag cement is manufactured using ground granulated blast furnace slag. The slag is a very useful latent hydraulic material to combat the deleterious alkali-silica reaction in concrete in structures. The granulated slag as per IS:12089[10], a by-product of iron manufacture consists essentially of glass containing silicates and aluminates of lime. The glass content of the granulated slag is about 90%.The Portland slag cement with 50-55% g.g.b.s and maximum alkali content of 0.9% (as Na2O equivalent) is ideal to combat the deleterious alkali-silica reaction in mass concrete structures e.g hydro-electric projects’ structures or any underground foundation structures e.g structures in sea or in coastal areas or in marshy land, as moisture is always available in these places, for reaction to take place inside the concrete. The reaction is also fast, as the fineness of Portland slag cement is high, generally more than 300m2/kg. The reaction product is calcium silicate hydrate, which is continuously increasing inside the concrete, and the resulting microstructure of concrete is dense. Thus, the long-term strength of PSC concrete is higher and higher with time. The impermeability of concrete is so high that, no aggressive agent can enter inside the structures.

In our construction industries specially hydro-electric projects, the above recommendations should be followed. In some project sites, the PSC having slag content of more than 50% (i.e 56 to 70%) is being used, as this is permitted by the Indian Standard IS455. In such cases, the alkali content of PSC is also going to be higher than 0.9%. Such PSC may be useful to combat the chlorides and sulphates in soil and ground water specially in coastal areas, but for hydro-electric projects ,they should not be used. This is because, higher than 0.9% alkali in PSC may not be able to combat the deleterious alkali-silica reaction (if any).

International Recommendations
Pozzonalas like flyash containing alkalies not more than 2% or 3% has been found effective in combating the alkali-silica reaction. Pozzolanas in the concrete mix are beneficial, because they reduce permeability of concrete and therefore reduce the mobility of aggressive ions, present within concrete and which may ingress{11]. G.G.B.S is also effective in mitigating the deleterious alkali-silica reaction in concrete. There is evidence that , when PSC has been used, a maximum alkali content of 0.9% is harmless, when the slag content of the cement is not less than 50%[12].

In the Netherlands, CUR-Recommendation indicates that if cement replacement by at least 25% flyash or 50% g.g.b.s is implemented, then the potential reactivity of the aggregates is of no concern[13]. In the Netherlands, the deleterious expansion in a no. of structures was observed. But it was absent where PSC had been used[14]. Malber et al [15] recommended use of low alkali OPC and cement replacement of 25to40% classF flyash or 40 to 50% g.g.b.s . They discouraged the use of 15% flyash , as it may worsen the ASR expansion, even with classF flyash.

ICOLD Bulletin no.79[4] states that there is now considerable experience of the use of PSC with some types of reactive aggregates, and there is no known instances of deleterious alkali reactions, when the PSC contained more than 50% slag and the slag has less than 0.9% alkali, as Na2O equivalent. The Bulletin does not recommend PPC in minimizing the risk of alkali-aggregate reaction , because of the variability in their properties.

Conclusions and Recommendations
Alkali of cements, although a minor component, plays an important role for durability of concrete. OPC having alkali less than 0.6% (as Na2O equivalent) is considered to be low-alkali cement, because if such cement is used in concrete, the deleterious expansion due to alkali- silica reaction is not likely to occur. The alkalies of PPC and PSC are not fully reactive. Only about 17% of the alkali of flyash and about 50% of the alkali of g.g.b.s are reactive. PSC with more than 50% slag and having less than 0.9% alkali as Na2O equivalent is considered to be “Low alkali” cement by ICOLD.

For combating the deleterious alkali-silica reaction in concrete, IS455 recommends a maximum alkali content of 0.9% as Na2O equivalent, for PSC having minimum slag content of 50%. PSC with higher than 50% slag (i.e with 56 to 70% slag), the alkali content will be higher than 0.9%. Such high-alkali PSC may not be suitable for use in concrete, to combat the deleterious alkali-aggregate reaction (if any). The International Commission on large dams ICOLD does not recommend PPC for combating the deleterious alkali-aggregate reaction, because of its variable properties.

All the aggregates are not reactive. Some Himalyan aggregates are reactive. It is not possible to test every cubic meter of aggregate. Therefore, precautions should be taken in concrete construction i.e in vulnerable cases, e.g in hydro-electric project structures, which are mostly located in hilly regions, underground foundations of concrete structures, structures in sea, in coastal areas, and in marshy land, where reactive aggregates may be there and at the same time, moisture is available for the reactions to take place inside the concrete, by using PSC with 50-55% slag and having alkali content (as Na2O equivalent) of maximum 0.9%, so that the satisfactory service is obtained for the designed service lives of the structures.

References
  1. Irrigation Department, Uttar Pradesh. Rihand Dam Expert Committee Report, Vol.1,June 1986,58p.
  2. Z.Owslak, J.Zapala-Slaweta, and P.Czapik. Diagnosis of concrete structures distress due to alkali-aggregate reaction. Bulletin of the Polish Academy of Sciences,Vol.63,No.1,2015.
  3. J.A.Forney and B.Kerkhoff. Diagnosis and control of alkali-aggregate reaction in concrete. PCA R&D Serial No.20716, Portland Cement Asssociation,USA,2007.
  4. Seung-Ho Hong, Seung-Hwan Han and Kyong-Ku Yun. A case study of concrete pavement deterioration by alkali-silica reaction in Korea. International Journal of Concrete Structures and Materials, Vol.1, No.1, December2007, pp.75-81.
  5. ICOLD. International Commission on Large Dams. Alkali-Aggregate Reaction in Concrete Dams. Review and Recommendations. Bulletin No. 79, 1992.
  6. BS 5328: Part4:1990.Specification for the procedure to be used in Sampling, Testing and Assessing Compliance of Concrete.British Standards Institution,London.
  7. BRE. Building Research Establish- ment Digest 330. Alkali aggregate reactions in concrete. Building Research Station, Garston, Watford.
  8. IS 455. Indian Standard Specification for Portland slag cement, Bureau of Indian Standards, New Delhi.
  9. IS 1489(Part1). Indian Standards Specification for Portland pozzolana cement. Bureau of Indian Standards, New Delhi.
  10. IS 12989 Indian Standards Specification for granulated slag for the manufacture of Portland slag cement. Bureau of Indian Standards, New Delhi.
  11. A.M. Neville. Properties of Concrete. 5th Edition,2013, Pearson Education Ltd.
  12. W.H.Duda. Cement Data Book.2, Berlin, Verlag GmBH , 1984, 456p.
  13. V.Jensen and B.Fournier. Influence of different procedures on accelerated mortar bar and concrete prism tests: Assessment of seven Norwegian alkali-reactive aggregatyes. 11th Conference on alkali-aggregate reaction, Quebec, Canada, 2000, pp.345-354.
  14. W.M.M. Heunen. Alkali-aggregate reaction in the Netherlands. Proceedings, 9th International Conference on alkali-aggregate reaction in concrete, London, Vol.1, pp.432-437.
  15. L.J.Malvar, G.D. Cline, D.F Burke, R.Rollings, T.W.Sherman and J.L.Greene. Alkali-Silica Reaction Mitigation: State –of –the-Art and Recommendations. ACI Materials Journal, September-October 2002, pp.480-489.
International Concrete Construction Technology, March - April 2023
Fabric Reinforced Cementitious Matrix: Structural Strengthening Systems

Fabric Reinforced Cementitious Matrix: Structural Strengthening Systems

The need for structural strengthening in aging infrastructures is rapidly escalating across various sectors, encompassing buildings, industrial structures, bridges, dams, ports, and other important structures. This demand extends

Read more ...

Assess Build Chem: Long-Lasting Solutions for Basement Waterproofing

Assess Build Chem: Long-Lasting Solutions for Basement Waterproofing

Assess Build Chem provides effective and long-lasting protection for buildings with its innovative products and solutions for deep/large basement waterproofing. Basement waterproofing is a crucial aspect of building construction, especially in

Read more ...

Dam Rehabilitation With Cutoff Wall for Seepage Control

Dam Rehabilitation With Cutoff Wall for Seepage Control

As storm damage becomes more severe and has occurred more frequently in recent years, addressing the needs to repair essential infrastructure and dam rehabilitation is also becoming more common. However, deep foundation experts and others

Read more ...

JOGANI Reinforcement: Alkali Resistant ARACC Coated Waterproofing Mesh

JOGANI Reinforcement: Alkali Resistant ARACC Coated Waterproofing Mesh

Jogani Impex is considered an industry leader in providing international grade Alkali Resistant ARACC Coated waterproofing mesh, which enhances the waterproofing systems and solutions in all types of buildings and structures, while saving money

Read more ...

Assess Build Chem’s Deep & Large Basement Waterproofing Solutions

Assess Build Chem’s Deep & Large Basement Waterproofing Solutions

Assess Build Chem, a leading provider of construction chemicals, is ensuring long-term protection of buildings with its innovative waterproofing solutions that include a 5-step waterproofing method for deep and large basements. Sunny Surlaker, Head

Read more ...

Agrani: Waterproofing, Retrofitting, Civil Work & Interior Fit Outs

Agrani: Waterproofing, Retrofitting, Civil Work & Interior Fit Outs

By adhering to the highest industry standards, Agrani Group has gained a reputation for delivering solutions waterproofing, retrofitting, civil work & interior fit outs that surpass client expectations, avers Ramendra Bahadur Sinha

Read more ...

FAIRMATE's FAIRFLO CRYSTALLINE: Waterproofing Admixture for Concrete

FAIRMATE's FAIRFLO CRYSTALLINE: Waterproofing Admixture for Concrete

FAIRMATE is catering to the Speciality Construction Chemical Industry by manufacturing a complete range of construction chemicals like FAIRFLO CRYSTALLINE - Waterproofing Admixture for Concrete, along with cost-effective solutions and world-class

Read more ...

Nippon Paint India: Paints, Construction Chemicals & Waterproofing

Nippon Paint India: Paints, Construction Chemicals & Waterproofing

In line with its global vision, Nippon Paint India is expanding its portfolio beyond the paint and coatings product range; it will now offer products and solutions under the broad categories: Dry mix, Repair and Maintenance, Construction Chemicals, and

Read more ...

Retrofitting for buildings: Enhance structure lifespan & efficiency

Retrofitting for buildings: Enhance structure lifespan & efficiency

Despite understanding the potential of retrofitting and its distinct and far-reaching advantages in making existing buildings green and sustainable, retrofitting continues to be undertaken on a very limited scale; hence, it needs to be promoted and made mandatory

Read more ...

Cause of Distress of an Old Building Through Advanced Analysis

Cause of Distress of an Old Building Through Advanced Analysis

The technical service life of a reinforced concrete building is the time in service when structural safety is unacceptable due to either material degradation or exceeding the load carrying capacity, or both. In which case, the repair strategy may be adopted

Read more ...

Value Engineering with MCI®-2019 Water Repellent for Concrete Repair

Value Engineering with MCI®-2019 Water Repellent for Concrete Repair

True value engineering saves money without reducing service life or affecting the quality of construction or materials. Ideally, it adds value to the project. MCI®-2019 Water Repellent is one such value engineering solution that can extend

Read more ...

Agrani Milestone Use Carbon Fiber Laminates to Strengthen Slab

Agrani Milestone Use Carbon Fiber Laminates to Strengthen Slab

Ramendra Bahadur Sinha, Managing Director, Agrani Milestone, explains the remedial measures and challenges faced during slab strengthening of a deflected slab at IIT. NBCC India Limited undertook the strengthening of a deflected slab at a G+2 storey IIT building

Read more ...

Waterproofing Challenges & Remedial Measures in High Rise Buildings

Waterproofing Challenges & Remedial Measures in High Rise Buildings

High-rise buildings need special attention when it comes to waterproofing as the challenges inherent in them are peculiar in nature. Unfortunately, there is a lack of knowledge on the remedies and products available in the market as water- proofers continue to

Read more ...

Importance of Waterproofing Structures

Importance of Waterproofing Structures

The longevity of structures depends on how much resistance the building element will offer to water ingress. Water leakage not only reduces the durability but also hampers the serviceability or usability of the structure; hence, a good waterproofing system will

Read more ...

Terrace Waterproofing Solutions for Energy-Efficient Buildings

Terrace Waterproofing Solutions for Energy-Efficient Buildings

Terrace waterproofing is particularly important and is considered a priority as the roof is always exposed to harsh climatic conditions and weather changes. Rajeev Gupta, Business Head, ECMAS Construction Chemicals Pvt. Ltd. An effective waterproofing solution

Read more ...

Structural Rehabilitation of Reinforced Concrete Structures

Structural Rehabilitation of Reinforced Concrete Structures

Cement concrete is one of the most important construction materials and is practically basic to present-day developments. It is strong enough mechanically, yet vulnerable to deterioration. It thus gets damaged and even fails. This deterioration may be due to the weathering

Read more ...

Thermax - HDPE-SBS Waterproofing System for Basement Waterproofing

Thermax - HDPE-SBS Waterproofing System for Basement Waterproofing

Gradual shift in lifestyle has driven the idea of modern construction towards developing underground spaces and buried structures to bring efficiency in use of space. However, the improved efficiency comes with an increase in challenges like infiltration

Read more ...

Waterproofing in Hilly Areas with Sub-Zero Temperatures

Waterproofing in Hilly Areas with Sub-Zero Temperatures

Industry experts Kunjan Popat, General Secretary, Waterproofing Association of India; Ramendra Bahadur Sinha, Managing Director, Agrani Enterprises, and MS Sudish, Director, SIWIN Institute of Waterproofing and Insulation, share the challenges

Read more ...

Dow Sealants for Sustainable Infrastructure

Dow Sealants for Sustainable Infrastructure

Durability is a key requirement for modern infrastructure projects – highways and roads, bridges, airports and airfields, walkways and plazas, parking structures and stadiums. Miles of concrete must

Read more ...

To get latest updates on whatsapp, Save +91 93545 87773 and send us a 'Saved' message
Click Here to Subscribe to Our eNewsletter.