A multi-zone cementitious product, which includes a base zone made of a first cementitious material composition and forming a portion of the product. At least one facing zone is adjacent to and bonded to the base zone, the facing zone made of a second cementitious material composition and forming at least one exterior face of said product which is visible when the product is installed. A disrupted boundary layer is between the facing zone and the base zone, and includes material from both the facing zone and the base zone. The disrupted boundary layer bonds the facing zone to the base zone. The facing zone has a thickness sufficient to prevent the base zone from being visible when the product is installed.

The present description relates to a method of producing a wet-cast slag-based concrete product particularly where the wet-cast slag-based concrete product is partially or completely set inside a mould, pre-conditioned outside of the mould and then cured with carbon dioxide in a curing chamber. The wet-cast slag-based concrete product is optionally reinforced.

The invention provides novel aerated composite materials made from a carbonatable calcium silicate composition, and formulations and methods of manufacture and use thereof, in particular, the use of novel additive mineral compositions in the form of magnesium, magnesium salts or magnesium oxides, to improve physical chemical properties of low density concrete materials. The low density, aerated material is comprised of calcium carbonate (CaCO.sub.3) and silica (SiO.sub.2), as cured products of carbonatable calcium silicate compositions.

A method for curing cementitious articles includes flowing dry steam and carbon dioxide (CO.sub.2) simultaneously into a curing chamber containing a cementitious article. A relative humidity within the curing chamber may be between about 50% and about 70% and a temperature within the curing chamber may be between about 50 C. and about 70 C. A dry steam and CO.sub.2 mixture with a CO.sub.2 concentration between 2.5 vol % and 40 vol % is provided in the curing chamber and the cementitious article is cured for a duration between about 4 hours and 16 hours. Cementitious products cured with the method may have a CO.sub.2 uptake of greater than 15 wt % and a mechanical strength at least 10% greater than a cementitious product cured only in dry steam or CO.sub.2.

The method according to the invention for producing a prestressed concrete workpiece is characterized in that the prestress is created by a heat treatment, wherein the concrete and the reinforcement therefor are selected in such a way that, when cooling the concrete workpiece from an elevated temperature, the heat expansion coefficient of the concrete is less than that of the reinforcement, and in that, during cooling, the concrete and the reinforcement adhere sufficiently strongly to one another if, during cooling, the concrete is hydrated at least to such an extent in order to be able to expand the reinforcement on account of the different heat expansion coefficients, and in that the concrete, together with the reinforcement, is brought to the elevated temperature in such a way that and is hydrated during cooling at least to such an extent that it is prestressed by the reinforcement after cooling.

Systems for accelerated carbonation curing of a pre-cast cementitious structure may include an ejector and a curing chamber downstream of the ejector. The ejector may be operable to combine a lesser-pressure carbon dioxide containing stream from a carbon dioxide source with a greater-pressure steam to produce a mixed stream including at least steam and carbon dioxide. The mixed stream may have a pressure greater than the pressure of the lesser-pressure carbon dioxide containing stream. The curing chamber may be operable to receive the mixed stream from the ejector and contact the mixed stream with the pre-cast cementitious structure to cure the pre-cast cementitious structure. Processes for accelerated carbonation curing of pre-cast cementitious structures using the systems are also disclosed.

The present invention relates to a process for producing precast products in an airtight enclosure, which comprises the steps of a carbonation of pre-dried concrete precast units by feeding CO.sub.2 gas into a closed airtight enclosure under near ambient atmospheric pressure (psig between 0 and 2) and/or low pressure (between 2 and 15 psig) conditions, wherein said pre-dried concrete units have lost between 25 to 60% of their initial mix water content.

The invention provides novel articles of composite materials having hollow interior channels or passageways, or otherwise being hollowed out, and formulations and methods for their manufacture and uses. These hollow core objects are suitable for a variety of applications in construction, pavements and landscaping, and infrastructure.

Disclosed are methods and solutions for sealing and curing concrete and other cementitious materials using strontium containing, non-alkali, non-silica, chemical solutions. The strontium-based solutions can be placed in admixture with cementitious materials prior to molding and curing to create a final product, or the strontium-based solutions can be applied to newly created or existing cementitious material surfaces to improve the repellent and stain, resistant properties.

The invention provides novel aerated composite materials that possess excellent physical and performance characteristics of aerated concretes, and methods of production and uses thereof. These composite materials can be readily produced from widely available, low cost raw materials by a process suitable for large-scale production with improved energy consumption, desirable carbon footprint and minimal environmental impact.