Additive for grouts, its preparation and use

Improving additive for cement and related masses based on an inorganic binder, comprising an alkali extract of lignocellulosic materials, the extract being modified with a fatty acid or an oily ester thereof; a process for the preparation of such additive; and a method of using the additive in improving the hardening characteristics of a cement or related mass.

The present invention relates to an improving additive for grouts based on 
inorganic binders, for example cement and lime, and the invention also 
covers a process for the preparation of such additive and a method of 
using it to improve the hardening characteristics of grouts. 
In spite of the enormous importance of inorganic binders for the building 
industry, such as cement and lime, they are far from satisfactory from 
several aspects. Thus, they have as a rule too long curing time resulting 
in delay at the working sites and high mould costs by the day-long periods 
of time required for example for different cement products before 
de-moulding can take place. Moreover, cement and lime grouts or pastes are 
generally after hardening much too water-absorbing, which can result in 
bursting from freezing and this usually results in bad heat insulation. 
Furthermore, magnesia cement has the disadvantage that it is not resistant 
to ageing in view of dissolution of magnesium chloride. They also often 
show unsatisfactory binding characteristics in relation to other building 
materials, such as steel and wood, and to desirable lighter and more 
insulating ballast materials, such as straw, wood fibre, saw dust, turf 
and the like. The last-mentioned characteristic is particularly pronounced 
when dealing with so-called magnesia cement, which has encountered 
particular difficulties on the market. Straw obtained from ordinary crops 
the surface of which is protected by a wax layer, is especially repellent 
to binding to cement and especially to magnesia cement, which fact 
counteracts a more general use of this, in other respects desirable 
ballast and reinforcement material in different types of cement products. 
In attempts to remove the protective wax layer on straw by means of an 
alkali in order to improve the adhesion to cement, particularly magnesia 
cement, it has been found that the alkali-treatment results not only in 
dissolution of the wax layer but also in dissolution of other substances 
from the straw so as to expose the fibres thereof. The fibre mass thus 
obtained, after squeezing out the alkali and after washing, is an 
excellent reinforcement material for cement and lime grouts. 
However, it is not only the exposed straw fibre which is of interest. The 
alkali extract obtained has been found to constitute an improving agent 
for cement and lime grouts as well as products where such grouts are 
present as binders, the above indicated disadvantages being largely 
avoided and the area of use of the grouts being extended. This alkali 
extract improving agent is obtained not only by treatment of stalks of the 
different kinds of grain, but also of stalks from other similar straw 
plants, such as grass, reeds and the like. While this invention will be 
described primarily in connection with alkali-treatment of straw it must 
be noted that the invention covers the use of all kinds of lignocellulosic 
materials. With regard to straw one usually means the stalks remaining 
from mature threshed crop.

The present invention, which is further characterized in the appended 
patent claims, is therefore based on the extract of cellulosic materials 
obtained by treating such materials with alkali, suitably at room 
temperature. The material, such as straw, may be treated in the state as 
harvested, but it may be advantageous first to cut it into shorter pieces 
and possibly also subject the same to light mechanical crushing, for 
example between rolls in order to accelerate the digestion. 
The digestion takes place with alkali having a concentration of at least 
5%. (In this disclosure, if not otherwise indicated, all percentages are 
based upon weight). Stronger alkali than 20% does not give any shortened 
digestion time. From a practical point of view it is therefore most 
convenient to use an alkali of about 20%, but the extract obtained should 
before use in accordance with the invention be diluted with 4 to 5 times 
its volume of water in order to facilitate the subsequent mixing 
operation. By using a 5% alkali a useful extract is obtained after about 
24 hours at room temperature, whereas after about 36 hours also the fibres 
have been digested to a major extent. The corresponding periods of time 
when using 20% alkali is 6 and 18 hours, respectively. Heating when the 
treatment is carried out in an open vessel does not give any significant 
acceleration of the digestion. Contrary hereto the digestion is 
accelerated by crushing the stalks, for example between rollers, so that 
using 20% alkali, digestion to expose the fibres can be carried out in 2 
hours. When using 20% alkali a suitable proportion has been found to be 
15-20 kgs of straw per 100 liters of alkali. The extract obtained when 
using concentrated alkali has the consistency of a relatively thick fluid 
oil, the viscosity of which increases to a gel-like consistency if a 
longer period of digestion is used. This is one of the reasons that it 
should be diluted before the subsequent use. 
The alkali extract prepared as described above cannot as such be mixed with 
cement or lime grouts, since it immediately results in a reaction making 
the grout clotty to gravel-like. This reaction tendency must therefore be 
modified, which can be done simply by a kind of neutralization of the 
alkalinity of the extract. This neutralization or perhaps rather 
saponification is in accordance with the invention performed by means of 
fatty acids being in a liquid state at or slightly above room temperature, 
such as up to about 35.degree. C. However, the fatty acids need not be 
used as such since it has been found to work equally well with their oily 
esters, for example in the form of vegetabilic oils. Thus, excellent 
results have been obtained with rape oil, peanut oil, corn oil, sweet oil, 
olive oil and mustard oil. Suitable proportions of oil admixed into the 
alkali extract are about 2.5 to 5 volume parts of oil per 100 volume parts 
of diluted extract. 
Both soda and potash lyes are useful for the preparation of the alkali 
extract, but the potash lye has been found to be sufficiently more 
advantageous in that it makes the mortar more flexible and is less 
foaming, that potash lye is preferred spite of the high cost thereof. 
When preparing a paste or mass which is improved by using the extract 
according to the invention 3-10 percent by volume of extract are admixed 
into the water used, lower contents giving a reduced hardness and high 
contents giving an increased hardness with regard to the final product. 
In this disclosure the expression "grout" or "paste" is intended to cover 
all kinds of masses setting to form a solid structure. The usual binders 
in such mass are cement and lime, and when sand and gravel or crushed 
stone are intermixed with for example a cement paste they are held 
together in a dense structure which is called concrete. When sand alone is 
admixed with Portland cement the grout is a so-called mortar. It is the 
paste which determines most of the important engineering and chemical 
properties of the final concrete. 
Thus, in one aspect of the invention there is provided an improving 
additive for grouts or pastes, comprising an alkali extract of a 
lignocellulosic material, in which said extract has been modified with a 
fatty acid or an oily ester thereof. The acid or ester is suitably in a 
liquid state at or slightly above room temperature. 
In another aspect of the invention there is provided a process for the 
preparation of an improving additive for grouts or pastes, comprising 
treating a lignocellulosic material with an alkaline solution; 
recovering the the extract solution thereby obtained; and modifying the 
extract solution by treating same with a fatty acid or an oily ester 
thereof. 
According to a third aspect of the invention there is provided a method of 
improving the hardening characteristics of building grouts or masses based 
on an inorganic binder, comprising adding to the mass an improving 
additive as defined above. The inorganic binder used is preferably cement 
and/or lime. 
The improvement obtained by using the extract is primarily manifested by 
its effect on the hardening time or the so-called de-moulding time. 
Whereas the de-moulding time for ordinary Portland cement when used on the 
building sites normally is of the order of 7 days it can be shortened by 
admixing the modified extract according to the invention down to 2 days. 
With regard to magnesia cement the corresponding de-moulding time is 
shortened from about 2 days to about 4 hours. Adding the extract to 
ordinary lime paste results in a significant shortening of the drying 
time. By adding the extract to cement pastes they become more flexible, 
are easier to vibrate and give better filling of the moulds in for example 
prefabrication of different profiles. Moreover, the adhesion to ballast 
materials, is improved not only with regard to sand, gravel and shingle 
but also with regard to untreated straw, saw dust and wood fibre. The 
paste also adheres better to other building constructional materials, such 
as old concrete, steel, glass, brick and wood. The completely hardened 
final product is in all tested uses provided with a better, pore-less 
cement skin and an improved resistance to impact. Particularly with regard 
to magnesia cement the addition of the extract has been found completely 
to counteract the deterioration by dissolution of magnesium chloride, 
which would otherwise take place progressively. Repeated treatment of test 
bodies of magnesia cement in alternatingly hot and cold water for 7 days 
has not shown any dissolution of MgCl.sub.2 in the water and has not in 
any way decreased the compressive strength. 
A grout or paste of magnesia or Portland cement improved according to the 
invention may also advantageously be admixed with a synthetic binder 
consisting of equal parts by volume of polymeric acrylate and carboxy 
methyl cellulose (CMC). With regard to magnesia cement CMC is suitably 
dissolved in part of the magnesium chloride solution for use in the paste, 
whereafter the liquid acrylate is admixed and the mixture thus obtained 
admixed in the rest of the paste mixture. With regard to Portland cement 
CMC is digested in part of the water intended for the paste, the acrylate 
being then admixed and the mixture blended with the remaining constituents 
of the mortar. The amount of acrylate as well as the amount of non-aqueous 
CMC added is suitably about 5% of the water volume of the paste. In this 
way it is possible to considerably increase the ratio ballast material to 
cement in the paste, so that when using for example chips or fibres of 
wood, turf, straw and bark as a ballast it is possible by casting to 
manufacture wood-like products having a stabilizing cement skeleton, which 
products are excellently nailable and workable with cutting tools.