notes

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