Step 01
Sample properly
Soil samples are taken at foundation level and groundwater is sampled from the borehole after standing, in clean containers with no headspace, and kept cool in transit.
Chemical Testing
Ground chemistry decides how long your concrete and reinforcement last. In coastal Karachi that is not a formality, it is the difference between a structure that reaches its design life and one that does not.
Chemical Testing: what it actually tells you
Sulphate attacks hardened concrete. It reacts with the cement hydration products to form expansive compounds, which crack the concrete from within and let more sulphate in. The countermeasure is a cement type and a minimum cement content chosen against the measured sulphate class, which is why the test comes before the concrete specification rather than after it.
Chloride attacks the reinforcement instead. Once the chloride concentration at the bar exceeds a threshold, the passive oxide film breaks down and the steel corrodes, expanding and spalling the cover. Coastal and reclaimed ground around Karachi routinely carries enough chloride to make cover depth and concrete permeability critical.
We test both soil and groundwater, because the aggressive agent moves with the water. pH tells you how acidic the ground is, which affects both concrete and buried steel, and organic content matters because organic soils are compressible, slow to gain strength and can interfere with cement hydration in stabilised ground.
At a glance
- MatrixSoil and groundwater
- DeterminandsSulphate, chloride, pH, organic content
- TurnaroundTypically 3 to 5 working days
- OutputAggressivity class and concrete recommendation
How we run it
The sequence we follow on site and in the laboratory, and the point of each stage.
Step 02
Prepare extracts
Water soluble sulphate and chloride are determined on a 2:1 water to soil extract, with acid soluble sulphate run where total sulphate is required.
Step 03
Sulphate
Determined gravimetrically as barium sulphate or by ion chromatography, and reported both as SO4 and as SO3 to suit the specification in use.
Step 04
Chloride and pH
Chloride by titration against silver nitrate, pH on a soil water suspension with a calibrated electrode.
Step 05
Organic content
Loss on ignition or wet oxidation, reported as a percentage of dry mass.
What you receive
- Water soluble and acid soluble sulphate as SO4 and SO3
- Chloride content of soil and groundwater
- pH of soil and groundwater
- Organic content by loss on ignition
- Aggressive chemical environment class and the resulting concrete recommendation
When this test is the right one
- Before writing any concrete specification for foundations
- Coastal, reclaimed and industrial sites
- Buried steel, pipelines and ground anchors
- Where groundwater is shallow and in contact with the structure
- Where organic or made ground is suspected
Methods and standards
Every result is reported with its method reference and the calibration status of the instrument used.
BS 1377 Part 3 chemical and electro chemical testsASTM D4327 anions by ion chromatographyASTM D4972 pH of soilsASTM D2974 moisture, ash and organic matterBRE Special Digest 1 concrete in aggressive ground
Common questions
What engineers most often ask us about chemical testing.
Both, because specifications differ. BRE Special Digest 1 works in SO4, while some older specifications and cement standards use SO3. Reporting only one invites a factor of 1.2 error, so we give both and state which class the result falls in.
Yes where groundwater is within reach of the foundation. Mobile sulphate and chloride travel in the water, and a groundwater result is often more aggressive than the soil result from the same depth.
It drives the durability specification: lower water to cement ratio, greater cover to reinforcement, and in severe cases a change to the reinforcement itself or an applied protection system. It is far cheaper to design for it than to repair spalled concrete later.
Often ordered alongside
Most investigations combine several of these. We scope them together so you are not paying to mobilise twice.
Soil & Rock Testing
The laboratory is where samples become design parameters.
Read more
Concrete Testing
Concrete is specified by a strength it will not reach for 28 days, on a site where it is placed in minutes.
Read more
Electrical Resistivity Test
A non intrusive way to read the ground between boreholes, and the measurement earthing engineers and pipeline designers...
Read moreNeed chemical testing on your project?
Send us the location, the structure and your programme. You get a scoped quotation with the standard, the number of tests and the turnaround written into it.