If we do something to decrease the PH of concrete after mixing and molding, what will be the result? is the PH important parameter in concrete properties?is there any paper about this subject?please explain.
pH is the important parameter in studying the properties of concrete. Low and high pH both creates problem in concrete in terms of corrosion and spalling. For this ASTM has recommended 0.6% alkalinity of cement or mineral admixtures (if alkaline) for use in concrete.
High pH of the cement is due to presence of portlandite (CaOH2) and after adding in concrete mix the pH of the concrete decreases after setting due to utilization of portlandite in the formation of hydration products like CSH, ettringite and others. This formation of CSH and other hydration products dense the matrix and reduces the permeability of the chloride or reduces the carbonation resulted in reduced corrosion.
Several studies have been reported on the use of mineral admixtures (like SCMs etc.) that reduces the high alkalinity of cement-concrete, fills the voids and hardens the matrix leads to reduction in porosity and/or permeability. The addition of SCMs decreased the pH or alkalinity up to certain limit that is necessary for hydration reaction and additional supply of Al, Si from the admixtures enhance the formation of additional hydration products.
The decrease in pH of the concrete mix before casting and molding affects the early hydration and strength but improves the later age concrete properties.
Decrease in ph induces chloride attack and spalling of concrete as concrete is highly alkaline material......ultimately this will cause corrosion. Carbonation is major cause of decrease in Ph value.
pH is the important parameter in studying the properties of concrete. Low and high pH both creates problem in concrete in terms of corrosion and spalling. For this ASTM has recommended 0.6% alkalinity of cement or mineral admixtures (if alkaline) for use in concrete.
High pH of the cement is due to presence of portlandite (CaOH2) and after adding in concrete mix the pH of the concrete decreases after setting due to utilization of portlandite in the formation of hydration products like CSH, ettringite and others. This formation of CSH and other hydration products dense the matrix and reduces the permeability of the chloride or reduces the carbonation resulted in reduced corrosion.
Several studies have been reported on the use of mineral admixtures (like SCMs etc.) that reduces the high alkalinity of cement-concrete, fills the voids and hardens the matrix leads to reduction in porosity and/or permeability. The addition of SCMs decreased the pH or alkalinity up to certain limit that is necessary for hydration reaction and additional supply of Al, Si from the admixtures enhance the formation of additional hydration products.
The decrease in pH of the concrete mix before casting and molding affects the early hydration and strength but improves the later age concrete properties.
Decreasing of PH detrmines loss of alkaline protection of rebars.
Corrosion of bars can happen, due to carbonation, humidity, and or chlorides attack.
"If we do something to decrease the PH of concrete after mixing and moulding, what will be the result?"
Depends on the way you want to lower the pH of the concrete? If you use carbon dioxide you are adding material to your concrete. The matrix becomes a higher density and with it a slightly better compressive strength. As mentioned above the big disadvantage is the loss of rebar protection. If this is no problem for your investigation...
If you are going to dilute the alkaline you are taking material from your matrix. The matrix density decreases. I know concrete wall surfaces from drinking water facilities which could be removed up to 2 cm deep by using my finger.
Decreasing the pH level signifies the increase of acidity in the concrete. Thus, corrosion of reinforcement bar in the concrete will occur which degrades the concrete strength. There are few papers out there which discuss on the relationship between corrosion of concrete, concrete strength and even the effects in construction later on.
pH level is extremely important in concrete mix. Among other effects, it affects the reinforcements and then the durability of concrete.
Corrosion of rebar may damage reinforced concrete. When rebar corrodes, the oxidation products (rust) expand and tends to flake, cracking the concrete and unbonding the rebar from the concrete
http://en.wikipedia.org/wiki/Reinforced_concrete
https://www.researchgate.net/post/What_is_the_effect_of_less_alkaline_cement_on_corrosion_in_reinforced_concrete
Decreasing the pH level signifies the increase of acidity in the concrete. Thus, corrosion of reinforcement bar in the concrete when pH value is less than 7 will increase the action of corrosion .
what about if we don't allow to decrease PH less than 7, but around 8 or 9?
In concrete media, the pH lowering from 12.5 cause the decrease of pore liquids acidity and thus decrease of unstability of hydration product. This phenomena in first hour, lead to accelerate of ettringate large crystals and low strength even in early age and durability problems in long term. Decrease of pH also cause to decrease the amount of calcium carbonate and decrease the reaction rate of produce of CSH as hardening element in concrete. It is clear if the pH decrease, be larger, the destructive effect is more and lead to formation of very porous concrete with low strengh
Hi Maryam, can you suggest some research papers which discuss on relation between rate of strength development/ durability and pH of concrete or mortar ?
Thank you.
That will lead to more corrosion of steel bars in reinforced concrete and dissolving of main phases in cement matrix.
Using some chemical additives decreases the PH in the concrete same as pozzolanic additives , decreases the amount of the caOH2 in the concrete matrix leads to decrease the PH , you ask if it's good , that depends on your applications , some metals are stable in high ph environment (steel bars .. ) and others not (aluminum , Tungesten ... ) .
Concrete PH is generally aroun 12 (very basic). It is good to protect reinforcement from corrosion. If PH decreases to neutral (like 7) the ambient becomes favourable to steel corrosion, so it becomes dangerous. Aa common phenomenom called carbonation can cause this decrease in PH. Also using de-icing salts or maritime environment can cause the same problem.
please suggest some research papers regarding PH related concept of concrete
Surface tension of gel water of concrete highly depend on pH of concrete( Around 12).If we reduce the pH of concrete ( By reducing the quantity of CH form during the hydration of concrete) by any medium, it reduces the surface tension of gel water and gel water may be leached out ultimately porosity of concrete increases, strength and durability of concrete will reduces.
- Badges
- Science topic