Poaceae fibres and building products

A dry binder mix which is ready to use after addition of water, said mix comprising at least (A) a silicon containing hydraulic binder and (B) chemically modified unpyrolyzed ageing resistant fibres selected from the group consisting of Miscanthus-like species, Pennisetum-like species, Zea-like species and mixtures thereof, said ageing resistant fibres having a length comprised between 2 and 100 mm, said ageing resistant fibres having a water content of less than 20% by weight, said ageing resistant fibres having a coating obtained by contacting initial fibres with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibres contacted with said treating aqueous dispersion;

• whereby said coating of said ageing resistant fibres comprises at least (a) aminosilane bound to silicon atoms present in said ageing resistant fibres and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of the surface treating mixture is comprised between 5:1 and 20:1,
• wherein said ageing resistant fibres keeping during a storage period for 6 months in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibres after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K2O weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%.

A building product comprising at least a part or layer comprising a hardened silicon containing hydraulic binder containing chemically modified unpyrolyzed ageing resistant fibres selected from the group consisting of Miscanthus-like species, Pennisetum-like species, Zea-like species and mixtures thereof,

• wherein said ageing resistant fibres having a length comprised between 2 mm and 100 mm, said ageing resistant fibres having a water content of less than 20% by weight, said ageing resistant fibres having a coating obtained by contacting initial fibres with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibres contacted with said treating aqueous dispersion;
• whereby said coating of said ageing resistant fibres comprises at least (a) aminosilane bound to silicon atoms present in the fibres and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of said surface treating mixture is comprised between 5:1 and 20:1,
• the said ageing resistant fibres keeping during a storage period for 6 months in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibres after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K2O weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%.

A method for the preparation of a building product, said method comprising at least the steps of:

• (1) mixing together at least
• (A) chemically modified unpyrolyzed ageing resistant fibres selected from the group consisting of Miscanthus-like species, Pennisetum-like species, Zea-like species and mixtures thereof, said ageing resistant fibres having a length comprised between 2 and 100 mm, said ageing resistant fibres having a water content of less than 20% by weight, said ageing resistant fibres having a coating obtained by contacting initial fibres with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibres contacted with said treating aqueous dispersion;
• whereby said coating of said ageing resistant fibres comprises at least (a) aminosilane bound to silicon atoms present in said ageing resistant fibres and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of said surface treating mixture is comprised between 5:1 and 20:1,
• wherein said ageing resistant fibres keeping during a storage period for 6 months in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibres after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K2O weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%,
• (B) a hardenable calcium containing hydraulic binder, and
• (C) water,
• to form a hardenable fibres containing mixture;
• and
• (2) hardening said hardenable fibres containing mixture at a temperature greater than 20° C.

A method for preparation of chemically modified unpyrolyzed ageing resistant fibres selected from the group consisting of Miscanthus-like species, Pennisetum-like species, Zea-like species and mixtures thereof, said ageing resistant fibres having a length comprised of between 2 mm and 100 mm, said ageing resistant fibres having a water content of less than 20% by weight, said ageing resistant fibres having a coating obtained by contacting initial fibres with a treating aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising (a) OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, and (b) an amino coupling agent, and drying said initial fibres contacted with said treating aqueous dispersion down to a water content of less than 20% by weight;

• whereby said coating of said ageing resistant the fibres comprises at least (a) aminosilane bound to silicon atoms present in said ageing resistant fibres and (b) polydimethylsiloxane bound to aminosilane group via a silanol group,
• whereby the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of the surface treating mixture is comprised between 5:1 and 20:1,
• wherein said ageing resistant fibres keeping during a storage period for 6 months in an air environment having a temperature of about 20° C. and a relative humidity of 50%, an alkali resistance in a 1 N NaOH solution for at least 28 days of more than 92%,
• in which said ageing resistant fibres after complete burning at 600° C. have an ash characterised by a SiO2 weight content comprised between 41% and 70% and a K2O weight content comprised between 4% and 24%, while the SiO2+K2O weight content of said ash is comprised between 68% and 85%,
• said method comprising at least the following steps:
• determining, after complete burning at 600° C., an average SiO2 content of the ash of at least one sample of fresh fibres containing plant parts from plants selected from the group consisting of Miscanthus-like species, Pennisetum-like species, Zea-like species and mixtures thereof, intended to be harvested,
• in case the determined average SiO2 content of said ash of said at least one sample of fresh fibres containing plant parts from plants selected from the group consisting of Miscanthus-like species, Pennisetum-like species, Zea-like species and mixtures thereof, is greater than 30% by weight, harvesting fresh fibres containing plant parts;
• cutting said fresh fibres containing plant parts into plant fibres with a length comprised between 2 mm and 100 mm;
• drying said cut plant fibres at a temperature of less than 75° C., so as to obtain dried plant fibres with a water content of less than 20% by weight;
• treating said dried plant fibres with an aqueous dispersion comprising less than 1% by weight of a surface treating mixture comprising OH terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000, an aminosilane coupling agent, and a polyethylene glycolether, in which the weight ratio between said OH-terminated silanol terminated polydimethylsiloxane having a molecular weight comprised between 200 and 1000 and said amino silane coupling agent of the surface treating mixture is comprised between 5:1 and 20:1, so as to obtain humid coated plant fibres;
• drying of said humid coated plant fibres for obtaining said ageing resistant fibres with a water content of less than 20% by weight.