In brief
- An admixture is a chemical added to concrete in small doses, and its effect depends on the dose, the cement and the temperature, so it must be trialled before use.
- Ask the supplier for the batch or delivery sheet and the dose range, and ask the engineer to confirm the dose against the project specification.
- Waterproofers and accelerators sold in bulk without a label or dose sheet should be left out of structural concrete.
Contents
Admixtures reach Somaliland sites through two routes: branded pails and drums sold by the cement importer, and unlabelled jerricans mixed by local traders. Treat the second group as unknown until a trial mix and the project engineer say otherwise.
What is an admixture and which types reach Somaliland sites?
An admixture is a chemical dosed into a concrete mix in small amounts to change how it behaves, and the types seen on Somali sites are plasticisers, retarders, accelerators and waterproofers. Each works only within a stated dose range, and outside that range it can damage the concrete.
Plasticisers and superplasticisers let you reach a workable slump with less batch water. Retarders hold back setting in hot weather, which has to be balanced against early strength. Accelerators speed up setting and gain, useful where formwork has to come off sooner. Waterproofers aim to cut permeability.
The effect depends on the cement, the aggregate, the mix proportions and the concrete temperature. A dose that works with one cement may over-retard or flash-set with another. The supplier's data sheet and the batch sheet state a dose range for a reason, and that range is a general guide, not a local rule. Ask the engineer to confirm the intended dose against the project specification before anyone opens the container.
On site, decant the day's dose into a marked jug rather than pouring by eye. Keep a written record of what went in, how much, and the slump and set times that followed.
How do you check a delivery of admixture on site?
Ask for the batch sheet, the manufacture and expiry dates and the recommended dose, then photograph the container label and file it with the pour record. Open every pail before accepting it and look for separation, skinning, gel or a settled layer that will not stir back in.
Check the label first. It should name the product, the manufacturer, the batch number, the date of manufacture and the dose range. If the label is missing or unreadable, ask the supplier for the batch sheet before unloading. Print a photograph of the label for the file.
Open the container and look. A plasticiser that has separated into layers, formed a skin or gelled may not stir back to a uniform liquid, and a settled solid layer is a sign the product has frozen, overheated or aged past its shelf life. Do not accept a container you cannot mix back to a uniform colour and consistency.
Check the store. Admixtures are usually kept out of direct sun, above the floor on pallets and sealed against the rain. Follow the supplier's storage temperature range on the label. If the product has a shelf life, write the month of opening on the container, not the delivery month.
If the delivery is for structural concrete, ask the engineer or the client's clerk of works to sign the batch sheet into the pour file before batching starts.
How do you trial an unfamiliar admixture before the pour?
Make a trial mix with the exact cement, sand and aggregate that will go into the pour, then compare slump, working time and set against the same mix without the admixture. Until that comparison is on paper, the dose is a guess.
Use concrete calculator to fix the trial batch quantities with every assumption shown, then scale the same proportions into a small trial. Mix two batches at the same water content: one plain, one dosed at the supplier's recommended rate. If the dosed batch sets or stiffens noticeably faster or slower than the plain batch, or bleeds or segregates, record that and stop.
Run the trial at the time of day the pour will happen. A retarder that gives a comfortable two hours in the morning may give less at midday. Note the concrete temperature and the slump of both batches at mixing, at 30 minutes and at 60 minutes, and write the numbers into the pour file next to the dose used.
If the trial mix looks wrong, the batch team has two options: adjust the dose within the supplier's stated range, or drop the admixture and rely on the mix design. Never top up an over-retarded mix with extra cement or water to fix it. Ask the engineer to decide which option the specification allows.
For quantities on the full pour, run the agreed mix through the construction material calculator rather than scaling from the trial by eye, and record the admixture dose per cubic metre in the same sheet as the cement, sand and aggregate figures.
What to do next
Before the next structural pour, ask the supplier for the batch sheet of every admixture on site, check the label and expiry date on each container, and ask the project engineer to write the approved dose and the trial mix result into the pour file. Keep that file, the label photographs and the trial slump readings together.
For receiving discipline on cement, steel and blocks, see materials and the site's guidance on construction in Somaliland.
Frequently asked questions
Can I use an unlabelled waterproofer if the mason says it works?
Only if the supplier can name the product, show a batch number and give a dose range, and the engineer approves a trial mix with the cement and aggregates for that pour. Without those three things there is nothing to check.
What should the delivery record for an admixture contain?
Product name, manufacturer, batch number, manufacture and expiry dates, quantity delivered, recommended dose, the date the container was opened and who accepted it. A photograph of the container label filed with the pour record covers most of this.
Sources
Local reporting: this article is written for building work in Somaliland. Ground conditions, prices and rules differ between places; confirm the details for your own site.