Chemistry and mineralogy of the raw material.
Manufacturing and finished products chemical and mineralogical data.
St. Astier Natural Hydraulic Limes (NHL) are 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. 15 square miles) derives from crustacean deposits (chalky
limestone) infiltrated by silica but untouched by clay. Exploited for thousands of years, industrial production
begun in 1851. The quarries, owned by the same group from the industrial beginning, extend for 75 acres.
Tests conducted by the French government show a unique uniformity in the composition of the deposits (up to 300 feet in depth).
Chemical and mineralogical analysis of the deposit.
Chemical Analysis   
%
The absence of clay infiltration and the consequent minimal presence of Al2O3, sulphates and alkalis ensures the production of hydraulic limes based almost totally on the combination of Calcium Oxide and reactive silica.
Loss at ignition
40
CaO
44
SiO2
13
MgO
0.6
Al2O3**
1.1
Fe2O3**
0.32
SO3 **
0
Na2O **
0.04
K2O **
0.1
Others**
0.84
Corresponding mineralogical composition
H2O (moisture content)8The soluble silica, available to be combined with the CaO produced in the burning of the CaCO3) determines the hydraulicity of the finished products.
CaCO375
SiO2 (soluble)11  reactive/combinable
SiO2 (insoluble) 2   inert/un-combinable
MgCO31
Others (derivatives from items marked ** above)3
 
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 St. Astier NHL products are amongst the very few traditionally produced limes. The scientific knowledge of the manufacturer and modern quality control have, however, the favourable 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 produce the hydraulic performance of the finished products. Burning takes place in vertical kilns at temperatures not above 1850oF. 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 (#150). As shown below, the amount of potentially damaging components produced is so minute that adverse reactions, leading to materials deterioration, are not possible.
Composition CHEMICAL (%) MINERALOGICAL (%)
 NHL5NHL3.5NHL2   NHL5NHL3.5NHL2
Loss @ Ignition
161820     
Calcimetry (CaO2)10116     
Insoluble 5.69.68 

5.69.68
 CaO
595663 Free lime Ca(OH)2222558
Calcium Carbonate
CaCO3 UNBURNT
23
25
13
SiO2
15126  Calcium Silicate   
Combined C2S433517
     C3A0.70.50.4
Al2O31.921.661.3C2AS1.31.00.8
Fe2O30.570.490.4 C4AF0.70.50.4
SO3** 0.410.450.31 CaSO40.70.80.5
Others
MgO1.010.980.75 The quantities of these components are so small that their mineralogical presence is too minute to be relevant. Very significant for the alkalis (K2O/Na2O) which, even in small quantities (1.5/2% as in ordinary cement) can produce ALKALI  SILICA reactions.
MnO0.020.01>0.01 
TiO20.180.160.12 
K2O0.210.160.12 
Na2O0.070.060.04 

** 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.