Bioconstruction Prefabricated Elements Composed of Recycled Materials and Modified Calcium Sulphate

As a starting point, we use additives developed by the Engineering Department which, when mixed with calcium sulphate, improve its properties. The latest patented additive developed is a plasticising, superplasticising and gypsum-setting retarding agent that can be added in either solid or liquid form, acting on the setting process.

This and other additives under development are used at proportions ranging from 0.06 g/kg to 1.2 g/kg, with controlled setting times of between 15 and 240 minutes. The cost of this additive is estimated at €6/kg.

The amount of water used for mixing is also variable, depending on the intended purpose. One example is the possibility of using a minimum of 0.2 kg of water per 1 kg of gypsum. This produces a granular compound. If the amount is increased to 0.3–0.5 kg of water per 1 kg of gypsum, a gypsum mixture suitable for casting is obtained.

In terms of mechanical strength, compressive stresses of up to 19 N/mm² have been achieved.

Another application in which improvements have been obtained is the production of load-bearing elements for floor slabs, using gypsum with common reed. These models are based on traditional construction methods in the Mediterranean region, with certain design improvements. Increases in flexural strength of up to 116.2% compared with the traditional model have been achieved, based on improved adhesion between the contacting surfaces of the gypsum and reed. This results in significantly lower material consumption, as well as a lower carbon footprint. Several patents have been obtained for some of these improved designs.

This modified gypsum has also been applied to the coating of elements exposed to direct fire (achieving a fire resistance rating of 240 minutes for 4 cm thickness); for pressure-wave absorption (explosions of up to 84 kg of TNT located 3 m from the point of impact); and in the development of composite materials (vermiculite, silica sand for use in desert countries, fibres, common reed, etc.).

The material, always referring to the gypsum matrix, has the following characteristics:

• Thermal insulation: due to its high thermal inertia and low thermal conductivity coefficient, it reduces thermal bridges and eliminates the cold-wall effect.
• Regulation of ambient humidity. Gypsum coatings breathe like a genuine skin, regulating temperature and promoting air circulation within the room. They therefore ensure a balanced humidity level by rapidly absorbing excess moisture and releasing it back into the environment when the air is drier.
• Fire protection. They are non-combustible, extend fire resistance, and do not release toxic vapours or smoke when exposed to fire. Gypsum plays an active role because, thanks to its water of crystallisation, it not only slows the spread of fire but also absorbs a considerable amount of heat. With a melting point of 1370 ºC and a softening temperature of 1250 ºC, it is chemically stable at high temperatures, making it a suitable material for fire protection.
• Acoustic absorption. They have a certain degree of elasticity which, together with their finely porous internal structure, makes them good acoustic absorbers, reducing reverberation and attenuating sound waves. The addition of vermiculite significantly improves this property, as sound waves strike the multidirectional flakes of expanded vermiculite, are reflected in multiple directions and absorbed by the microscopic structure of mineral air bubbles.
• Durability: gypsum is resistant to atmospheric agents and the passage of time.
• Gypsum is recyclable and biodegradable, with negligible energy consumption during production. Its use in construction can result in energy savings of up to 30% (98%, as indicated, compared with ceramics) in terms of energy consumption in any developed country, highlighting its strong environmental credentials.
• HEALTHY: Another aspect to consider is the extensive body of research showing the unhealthy conditions associated with other materials used for thermal and acoustic insulation.
• It is mechanically deformable, making it less rigid in response to seismic movements. This deformability compared with ceramics and cement is an advantage.

The range of materials has applications across diverse construction fields and sectors, with the primary aim of providing a high level of safety:

• Passive fire protection and coatings
• Explosion protection
• Thermal insulation
• Acoustic insulation
• Protection of storage spheres for flammable materials.
• Protection of ventilation ducts and installations.
• Compartmentalisation or insulation of spaces susceptible to fire and explosion, or conversely, spaces requiring protection from these hazards.
• Testing for fire-resistant insulation of aluminium profiles.
• Load-bearing floor-slab elements incorporating common reed macrofibres
• Partition walls, floors, suspended ceilings, decorative wall elements…

The developments can be applied in sectors such as general civil construction, banks, military and police facilities, refineries, fireworks factories, ammunition depots, hotels, warehouses, industrial facilities, public buildings, schools, auditoriums, etc.

Calcium sulphate is not an innovative invention. Its use dates back to ancient Egypt and it is still used daily in a multitude of applications. It is therefore necessary to clarify that the improvements introduced by the research team focus on enhancing the use of this material. To achieve this, it was necessary not only to understand the material, but also to modify the way in which it is used.

Additives that modify its properties by acting on the chemical reaction already exist on the market (BASF, Sika, etc.). What do we contribute, then? We focus on the use of additives (including the recovery of some historical ones) in order to establish economically viable formulations. In addition, we needed to control the amount of mixing water, as well as the time at which the chemical reaction takes place.

There are not many references on this type of application because “gypsum”, despite its wide range of uses, does not appear to be an innovative material.

By reducing the mixing water while maintaining an appropriate working time, calcium sulphate can be used in almost any situation and with additions of all kinds. In this way, we have re-established “gypsum” as an element capable of replacing ceramic bricks, increasing its mechanical strength to values that were previously not achievable and, consequently, establishing it as a material to be directly considered in the construction sector.

The level of maturity varies according to the specific application:

• Fire and explosion protection: TRL 9 (Available for immediate application).
• Mixtures with silica sand and vermiculite: TRL 4.
• Use of organic fibres (common reed): TRL 4.
• Pruning waste and recycled construction materials: TRL 3–4.

• Construction and Civil Engineering Industry.
• Bioclimatic and Sustainable Architecture.
• Security and Defence Sector.
• Prefabricated Element and Coating Manufacturers.
• Waste Management Companies (interested in material recovery).

José Antonio Flores Yepes – University Institute for Research and Innovation in Agri-Food and Environmental Sciences (CIAGRO)