Alkali-aggregate reaction is the reaction between the active mineral constituents of some aggregates and the alkali hydroxides in concrete. It is only harmful when it produces significant expansion. There are two main forms: alkali-silica reaction and alkali-carbonate reaction. Alkali-silica reaction, also known as ASR, causes cracking in concrete from the reaction between certain reactive minerals or rocks in aggregates and alkalis in cement. It can cause visible symptoms like cracking and pop outs, which are small fragment breakaways leaving shallow depressions. Alkali-carbonate reaction is influenced by factors like clay or calcite/dolomite content and crystal size in aggregates.

1. BY
AKRAM AFRIDI

2. Alkali-Aggregate Reaction
 Is the reaction between the active mineral
constituents of some aggregates and the
sodium and potassium alkali hydroxide in
the concrete
 Harmful only when it produes significant
expansion

3. FORMS OF ALKALI AGGREGATE
REACTIONS
Alkali silica reactions
alkali-carbonate reaction

4. Alkali silica reaction
ALKALI-SILICA REACTIVITY
(ASR) ALALKALI-SILICA REACTIVITY
(ASR)KALI-SILICA REACTIVITY
(ASR)

5. What is ASR?
Visual symptoms
 network of cracks
 Closed or spalled joints
 Relative displacement
 cracking of concrete from alkali
silica reactivity

6. Alkali silica reactions

7. Harmful Reactive Substances
Some potentially harmful reactive minerals, rocks, and
synthetic materials
Several of the rocks listed react very slowly and may
not show evidence of any harmful degree of reactivity
until the concrete is 20 years old
Only certain sources of these materials have shown
reactivity

8. Pop outs
 A pop outs is the breaking away of a small fragment of
concrete surface due to internal pressure that leaves a
shallow typically conical depression

9. Controlling ASR
Non reactive aggregates
Supplementary cementing materials or blended
cements
Limit alkali loading
Lithium based admixtures
Limestone sweetening(30 % replacement reactive
aggregates with crushed limestone)

10. Alkali carbonate reactions

11. Alkali carbonate reactions
Influencing factors
 Clay contents, or insoluble residue content, in the range
of 5% to 25%
 Calcite to dolomite ratio of approximately 1:1
 Increase in the dolomite volume
 Small size of the discrete dolomite crystals (rhombs)
suspended in the clay matrix

12. Alkali carbonate reactions
Controlling ACR
 Selective quarrying to avoid reactive aggregates
 Blend aggregates according to appendix in ASTM C 1105
 Limit aggregates size to smallest practical