Admixture for Precast FRP concrete
Posted by Alokjit on August 30, 2006
I am a small manufacturer of Precast Concrete article. I want to manufacture Fibre reinfoced polymer concrete Manhole covers, Drain Covers etc. Will you help me by giving information of ratio for Concrete, Polymer and what type admixure should be used for the same. We have used Sika admixture for so many projects and earlier we were your approved applicator in India. We done some job at the time of constructing Goa factory. Name: Alokjit Dey. email: dey_alokjit@rediffmail.com or jolienco_cal@yahoo.ca. Please response to question. With Regard. Alokjit
Dear Mr. Alokjit,
This has reference to your question regarding "Admixtures for Precast FRP concrete".
The most commonly used polymer to make polymer modified concrete is a latex polymer, which is added to the concrete during mixing. Generally, the solid content of the latex polymer is in the range of 40 - 55%. The dosage range of solid polymer latex in concrete is from 10% to 25% by weight of cement depending on the properties desired.
Addition of latex polymer increases the workability of the concrete, so the water to cement ratio should be reduced appropriately. If you are looking for a higher water reduction than what is achieved by using the latex polymer, you can use either a water reducing or high range water reducing admixture. For more specific details on the dosage of the polymer and admixture, please follow the suppliers/ manufacturer's recommendations.
Polymer modified concretes have good resistance to water and have good bonding properties, so they popularly used for repair jobs or waterproofing jobs (eg. basement waterproofing)
If you are planning to use polymer in concrete to just improve its resistance to water ingress, another economical alternative would be to use either an integral waterproofing compound or a superplasticizer and reduce the water to cement ratio of the concrete to improve its water tightness. You can also use materials like Fly ash and slag at appropriate levels, which also help to reduce permeability.
Thanks and good luck.
alkali silica reactivity
Posted by Mary Ann on August 4, 2006
What should be done to concrete placed on vertical structures 6 month ago that uses sand potentially reactive to alkali silica reaction?
Alkali silica reaction (ASR) is the reaction between the alkali contained in cement and silica containing aggregate. There are two parts of this equation. ASR does not necessarily have to be of concern if one of the constituents is missing. Using potentially reactive aggregate in conjunction with low alkali cement or slag or flyash does not necessarily have to lead ASR damage.
Another variable is the type of the structure and location. For ASR to happen moisture is required. If the structure (for example a concrete retaining wall) has continuous access to moisture then ASR damage is going to be more detrimental and treatment of the structure might be very expensive.
If the structure is accessible and exposed only to rain for example, than ASR can be slowed down by reducing the moisture penetration into the structure. There are "breathable" coatings available on the market that allow diffusion of moisture out of the structure but do not allow moisture to enter the structure. Applying such a coating to a structure that shows signs of ASR can reduce the rate of ASR. There are also Lithium salts available in the market that are used to reduce the occurrence of ASR, These product are available as admixtures for new structures or as spray applied products to be used in existing structures.
None of these products are final solutions that eliminate ASR, but can be successfully used to manage the risk of severe damage from ASR.
concrete roof
Posted by Robert on August 2, 2006
I want to roof a wood frame house with a 6 in 12 pitch with lightweight concrete. Has it been successfully done?
A 6 in 12 pitch roof is pretty steep. It would take a very stiff mix to be able to place it and not sag.
One alternative would be to precast panels for the roof.
I would consider cellular concrete for the weight considerations but I would first contact a roofer for more information on constructing a roof of this nature.
It may have been done successfully but my knowledge of roofing is limited.
