St Astier Natural Hydraulic Limes (NHL)

Chemistry and mineralogy of the raw material

~ Manufacturing and finished products chemical and mineralogical data –
Thermocromex is produced from the burning and slaking of a pure chalky limestone with siliceous content. No additions are made. They strictly conform to the French Norm NFP 15.311 and the European Norm EN 459 classifying NHL.
~ The limestone in the St. Astier basin (approx. 40 Km2) derives from crustacean deposits (chalky limestone) infiltrated by silica but untouched by clay. Exploited for thousands of years, industrial production began in 1851. The quarries, owned by the same group from the industrial beginning, extend for 300,000 square meters (30 hectares). Tests conducted by the French government show a unique uniformity in the composition of the deposits (up to 100 m. depth).

Chemical and mineralogical analysis of the deposit:

Chemical Analysis

Loss at ignition

CaO

SiO2

MgO

Al2O3*

Fe2O3*

SO3*

Na2O*

K2O*

Others*

%

40

44

13

0.6

1.1

0.32

0

0.04

0.1

0.84

  • The absence of clay infiltration and the consequent minimal presence of Al2‚O3, sulfates and alkalis ensure the production of hydraulic limes based almost totally on the combination of Calcium Oxide and reactive silica.

 

Corresponding Mineralogical Composition

H2O

(moisture content)

CaCO3

SiO2 (soluble)

SiO2(insoluble)

MgCO3

Others (derivatives from items marked * above)

%

8

75

11

2

1

3

Reactive/combinable

Inert/un-combinable

  • The soluble silica, available to be combined with the CaO produced in the burning of the CaCO3 determines the hydraulicity of the finished products.

The production of different types of Natural Hydraulic Limes from the same raw material deposits proves that hydraulicity depends on the amount of silica combined and not on the total amount present. The theory that hydraulicity depends on the total amount of “clay (or silica)” in the raw material is fundamentally flawed.

The production method is essentially unchanged from the one used since ancient times: limestone burned and slaked. It is therefore correct to say that Thermocromex is amongst the very few traditionally produced limes. The scientific knowledge of the manufacturer and modern quality control has, however, the favorable effect of producing reliable materials with constant performance.

The burning process: Its methods and the energy used are the determining factors in the quantity of silica that combines with Calcium Oxide (CaO) to form Calcium Silicates (CS) which produces the hydraulic performance of the finished products. Burning takes place in vertical kilns at temperatures not above 1832oF (1,000oC). The fuel is anthracite coal, imported from Wales due to its purity, as it produces the least residuals.
Continuous checks are made to measure the efficiency of the burning (CO2 tests) which are essential to regulate the hydration that follows.

Hydration (slaking): The controlled hydration process is so precise that virtually no quick lime (<1%) will be present at the end. The efficiency of the slaking process is such that only a small percentage of the slaked material has to be milled to achieve the desired granulometry (0.09mm). As shown below, the amount of potentially damaging components produced is so minute that adverse reactions, leading to materials deterioration, are not possible.

* The presence of SO3, absent in the raw material, is induced by the coal used in burning. The small level of it, however, is harmless. Higher gypsum (CaSO4) levels due to additions as in the case of ordinary cement or some other hydraulic binders can cause damage.

C3S can occur due to “high spots” in the furnace and also due to eutectic reactions caused by the presence of alkalis which lowers the fusion point.

 

EU Norms (EN 459 Mandatory testing program for Natural Hydraulic Limes

POWDERS

TEST NORM EN459 Values St Astier Values Frequency EU Norms St. Astier Frequency
Fineness EN196-6 residue by mass
0.09mm/0.2mm
<15%/<5%
5-7% daily Daily
Free water EN459-2 3.5<2 <2
Soundness
(Expansion)
EN459-2 <2 <1 once a day several times
per day
Bulk density
Kg/dm3
EN459-2 NHL3.50.5-0.9 0.61/0.65 monthly each product
batch

 

FINISHES (prepared with standard EU sand/ISO 679 @ 1:1 vol. ratio

Penetration EN459-2 >20mm >20mm monthly Weekly
<50mm <50mm
Setting time EN459-2 >1h/<15h >3h/<10h 2 per week 2 per week
Air content EN459-2 <20 <20 monthly monthly
Compressive EN459-2 28 days weekly continuously
Strength N/mm2
NHL3.5 3.5 to 10 3.5 to 6
SO3 EN196-2
content % 3* 0.45/0.65 monthly continuously
*up to 7% admissible if soundness is demonstrated at 28 days of water curing
Available EN459-2 NHL53% 15-20% weekly each product
batch
Lime minimum NHL3.59% 22-26% each product
batch
values NHL215% 50-55% each product
batch

Other tests regularly performed by the St. Astier Research & Development Dept:
CO2 contents after each burning to regulate slaking, Tensile strength, Elasticity moduli, Adhesion, Workability (flow table), Whiteness.

Ecological Evaluation of Lime Binders using Natural Lime

CO2 re-absorption comparison for Thermocromex compared with similar Portland cement: Lime Finish Mixes

Carbon Dioxide deficit for 1 Cubic Meter of finish.

Ecological Evaluation

Amount of CO2 in Kilograms Emitted and Recovered per KG of Binder in the production and use of typical finishes.

Binder Constituents for Cement Finishes in a 1:1:5 ratio. (KGs per M3) Binder Constituents for an equivalent St Astier Natural Hydraulic Lime Finish in a 2:5 ratio (KGs per M3)
Sources of Carbon Dioxide Portland Cement 240 KGs required High Calcium Lime 83 KGs required NHL 3.5 244 KGs required
Therms of energy used to produce 1 tonne of binder

900

650

550

A CO2 generated from Fuel

96.72

25.56

61.44

Base on coal requirements to produce 1 tonne of binder
B CO2 Generated from Material (De- Carbonization)

99.84

45.12

85.4

CO2 emission during manufacture
C Re-Absorbed by Material

Nil

44.4

65.88

CO2 re-absorption during curing and first 2 years
 CO2 Deficit – (A+B) – C KGs per M3 of material

196.56 + 26.28 = 222.84

80.96

 Value of CO2emission against re-absorption

* For further guidance, please contact Southwest Progressive Enterprises.