What is alkali reactive aggregate?
Alkali–aggregate reaction is a term mainly referring to a reaction which occurs over time in concrete between the highly alkaline cement paste and non-crystalline silicon dioxide, which is found in many common aggregates.
What are the factors that affect alkali-aggregate reaction?
The alkali-aggregate reaction is greatly promoted by a relative humidity of 80 % or more. Like all chemical reactions, AAR is affected by temperature. In general the rate of reaction and formation of gel will increase as the temperature rises.
What is alkali-aggregate reaction and how it can be controlled?
Alkali-silica reaction can be controlled using certain supplementary cementitious materials. In-proper proportions, silica fume, fly ash, and ground granulated blast-furnace slag have significantly reduced or eliminated expansion due to alkali-silica reactivity.
How do you reduce alkali aggregate reactions?
Recommended measures are: (1) limiting the total alkali content of the concrete (from portland cement and other sources) and (2) the use of supplementary cementing materials (SCMs) such as fly ash or slag. Minimum replacement levels are given for fly ash and slag.
How many type of alkali reactive aggregates are there?
two distinct types
There are two distinct types of alkali-aggregate reaction in concrete; these are (i) alkali-silica reaction (ASR), which involves the reaction of certain silica minerals within the aggregate, and (ii) alkali-carbonate reaction (ACR), which involves the reaction of carbonate minerals.
Is code for alkali aggregate reactivity?
IS 2386-7: Methods of Test for Aggregates for Concrete, Part VII: Alkali Aggregate Reactivity.
What are reactive aggregates?
Reactive aggregates are those that either expand or develop expansive by products when introduced to certain chemical compounds.
What happens in an alkaline reaction?
Alkali metals react with water to produce heat, hydrogen gas, and the corresponding metal hydroxide. The heat produced by this reaction may ignite the hydrogen or the metal itself, resulting in a fire or an explosion. The heavier alkali metals will react more violently with water.
What causes AAR?
Alkali aggregate reactions (AAR) occur when aggregates in concrete react with the alkali hydroxides in concrete producing a hygroscopic gel which, in the presence of moisture, absorbs water and causes expansion and cracking over a period of many years.
How do you test alkali silica reactivity?
Usually in laboratory testing, the alkali–silica reactivity of an aggregate is evaluated indirectly by measuring expansion of a specified cement-aggregate combination at a specified, often at an elevated, alkali content and a specified environment.
What is alkali silica reaction and name any 4 types of aggregate that causes ASR?
1 Alkali–silica reaction. Alkali–silica reaction (ASR) is a material degradation mechanism that occurs in concrete structures. ASR is a chemical reaction occurring between the reactive siliceous aggregate particles and hydroxyl ions of the pore solution in hardened concrete (Saouma, Perotti, & Shimpo, 2007).
Is alkaline acidic or basic?
As this diagram shows, pH ranges from 0 to 14, with 7 being neutral. pHs less than 7 are acidic while pHs greater than 7 are alkaline (basic).
Does alkaline neutralize acid?
Alkaline water has a higher pH level than that of plain tap water. So proponents say that it can neutralize acid in your bloodstream.
How do you reduce alkalinity in concrete?
Not allowing water access to the material and maintaining the concrete’s internal relative humidity below 80% will stop further gel growth and alkali-silica reaction. Accomplish this by applying a sealer such as paint or a moisture barrier to the concrete surface.
How do you test an alkali silica reaction in concrete?
What is alkali-silica reactivity and how is it avoided?
The alkali–silica reaction (ASR), more commonly known as “concrete cancer”, is a deleterious swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (i.e., non-crystalline) silica found in many common aggregates, given sufficient moisture.
What is the pH of vinegar?
2–3
Acetic acid makes vinegar mildly acidic, with a typical pH of 2–3.
Is vinegar acidic alkaline or neutral?
acidic
Vinegar is acidic. Vinegar’s pH level varies based upon the type of vinegar it is. White distilled vinegar, the kind best suited for household cleaning, typically has a pH of around 2.5. Vinegar, which means “sour wine” in French, can be made from anything containing sugar, such as fruit.
What happens when alkaline is mixed with acid?
If exactly the right amounts of acid and alkali are mixed, you will end up with a neutral solution. This is called a neutralisation reaction. Accurate neutralisation reactions can be carried out in a science lab in a process called titration. Neutralisation reactions are really useful.
What happens when an alkali reacts with an acid?
When an acid and alkali react together, they produce a salt and water: acid + alkali → salt + water . As you may know, water is neutral, so the acid and the alkali have come together to neutralise each other (to make a pH 7).
What are alkalis in concrete?
Alkali content is defined as the content of sodium oxide (Na2O) and potassium oxide (K2O) in cement.
What causes alkali-silica reaction in concrete?
Cause of alkali-silica reaction
ASR is caused by a reaction between the hydroxyl ions in the alkaline cement pore solution in the concrete and reactive forms of silica in the aggregate (eg: chert, quartzite, opal, strained quartz crystals).
How do you reduce alkali silica reactions in concrete?
What is alkali silica reactivity?
Alkali-silica reaction (ASR) is the chemical reaction that occurs between alkali cations and hydroxyl ions in the pore solution of hydrated cement paste and certain reactive silica phases present in the aggregates used in concrete.