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Additive manufacturing of alkali-activated materials currently attracts a lot of attention, because of the possibility to produce customized high-performance elements for a range of applications, potentially being more resource-efficient than conventionally produced parts. Here, we describe a new additive manufacturing process for alkali-activated materials that is based on selective laser-heating of lithium aluminate/microsilica slurries. The new process-material combination allows to manufacture elements with complex geometries at high building rates and high accuracy. The process is versatile and transferrable to structures of sizes differing by orders of magnitude. The mechanical strength of the obtained materials was in the range of values reported for conventional metakaolin-based geopolymers, and superior to what has been hitherto reported for alkali-activated materials produced by additive manufacturing. This mechanical performance was obtained despite the fact that the degree of reaction of the lithium aluminate and the microsilica was low, suggesting that significant reactions took place only at the surface of the microsilica particles.
The SPIN Project included workshops for young academics and building materials laboratories of the cement and concrete sector. Within the framework of the SPIN Project, plans were discussed for the conference 'Advances in Cement and Concrete Technology in Africa' that will take place in January 2013. A lecture on application rules for shotcrete construction was given by Prof. Regina Stratmann-Albert who took part in the courses as guest speaker. A short lecture was given by Akindehinde Ayotunde on the use of starch in cement-bound systems. Renato Rajzer talked about standard regulations for quality assurance during site operation. A workshop for an interlaboratory comparison took place with participants from all regions of Africa to test cement according to the standard series EN 196. The Round Robin test comprises the determination of the tensile bending and compressive strengths according to EN 196-1, of the water demand, the initial and final set, and the soundness according to EN 196-3 as well as of the fineness according to EN 196-6.
One-part (“just-add-water”) geopolymers are a new dass of mineral binders that are produced without the use of alkaline activating Solutions. Compared to conventional geopolymers, i. e. those activated by highly alkaline Solutions, much less is known about the one-part geopolymers ’ microstructure and with regard to their rheology.
In this work, the rheology of one-part geopolymers, produced from microsilica and sodium aluminate, with several SiO-flACOiratios and two different water/binder-ratios (w/b) were investigated qualitatively with a viscometer (mortar measuring cellj.
Absolute values of plastic viscosity and yield stress were determined with a double gap measuring cell. In addition spread flow tests were conducted. The aim was to classify the early behavior of geopolymer pastes and to compare it to ordinary Portland cement (CEM 142.5 R) pastes.
At moderate to high shear rates, the measured flow curves cotdd be fltted well by the Bingham model. With increasing silica content the yield stress increased. Up to a certain SiOi/Al2O3-ratio viscosity also increased with increasing silica content; however, at higher silica/alumina-ratios the viscosity decreased again. Higher w/b-ratios caused lower yield stresses and viscosities. Compared to Portland cement pastes, most of the considered geopolymers were signiflcantly stiffer. The results were further Interpreted in terms of pore solution viscosity and volume-based water to binder ratios (w/b) of the geopolymer pastes.
A silica-rich residue from waste-water treatment of chlorosilane production was tested for its applicability for the production of one-part geopolymers. The residue was blended with solid sodium aluminate, the blend activated with water and cured at 70 °C. The degree of reaction and strength were determined after 1,3, and 7 days. The reaction products were analyzed by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen Sorption, and small-angle X-ray Scattering (SAXS).
Until the third day of curing the degree of reaction of the residue reached 51% and the strength reached 8.9 MPa. The reaction product was identified as geopolymer containing zeolite A. The results thus confirmed that the residue may be used in the production of geopolymers. However, from 3 to 7 days of curing no further progress of reaction was observed and the strength slightly decreased.
It was observed that even harsh vacuum drying left some water, presumably zeolitic water and surface hydroxyl groups, in the hardened geopolymer, the volume fraction of the emptied pores was approximately 45%. The SEM and SAXS analyses showed the gel-like microstructure of the geopolymer with diameters of the gel particles of about 70 nm on average. In line with this colloidal particle size, the specific surface area of the geopolymer was measured by SAXS to be approximately 120 m2/g. On the contrary, nitrogen Sorption measurements yielded a specific surface area of only 13 mz/g and did not show the presence of micropores, which is attributable to the inaccessibility of the pores of the geopolymer and the zeolites for nitrogen at the measurement temperature.
For several years, optical measuring techniques play an ever increasing role in various areas of construction. Applications ränge from simple laser-based distance measurements up to the use of advanced camera Systems to assess shape changes of components. The advantages of such Systems lie in the ränge of non-contact respectively in non-destructive measurement and in the high required accuracy and reproducibility. The continuous improvement and development of sensors and laser sources also opens constantly new applications and areas of applications. Already established measurement methods and technologies can be further developed and adapted to modern requirements. At BAM it is a laser-based measurement System has been developed that is capable to measure the roughness of component surfaces in equal to already established methods.
The building situation in Africa is overwhelmed with high-priced materials and lack of adequate concrete technology, which provides a challenge in the concrete industry. Worldwide, cement and concrete experts are at the cutting-edge to sustainable, green and healthy but nonetheless high-performance concrete, which is more sustainable and safer than traditional methods of construction with clay and wood. Since concrete in Africa is rather a new construction material, this sustainability experience can offer the continent a unique opportunity to begin a constantly growing building sector with the newest state-of-the-art technology. This can be achieved without subordinating to existing standards by establishing a sustainable “African concrete technology”. The major challenge for most sub-Saharan countries is the deficiency of experts, which would be required to establish such state-of-the-art technology. Based on the examples of two African-European scientific networks—SPIN and LightSHIP—this paper presents possible solution strategies for the establishment of a scientific cooperation between Europe and Africa, with links to policy making bodies that can help accelerate the progress of cement and concrete industries in Africa.
Additive manufacturing (3D printing) of ceramics and other materials offers significant advantages compared to conventional production processes for several applications. While ceramics have been extensively investigated in this regard, additive manufacturing of geopolymers have received much less attention to date. In the present contribution we study a ‘standard’ metakaolin-based geopolymer, a fly ash-based geopolymer and a silica-based one-part geopolymer regarding their suitability for additive manufacturing via selective laser curing. Model geometries such as bars and cuboids could be produced by this route. After selective laser curing the specimens were additionally cured at 80 °C for 24 h. The specimens were studied by means of scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). SEM showed that the precursors in all geopolymers had reacted partially and geopolymeric gel had formed. XRD confirmed these results and additionally revealed that the crystalline byproducts (zeolites) in the one-part geopolymer differed from the byproducts observed in conventionally produced samples. This indicates that also the geopolymerization reactions differ between the two synthesis routes. The mechanical strength after selective laser curing and 80 °C-curing appeared to be highest for the metakaolin-based geopolymer. However, SEM also showed that a significant volume of macropores remained in most regions of all specimens, while some regions in the metakaolin-based geopolymer appeared to be significantly denser. These preliminary results demonstrate that selective laser curing offers potential for the production of geopolymers, but more research has to be undertaken to optimize the process.
Future lunar exploration will be based on in-situ resource utilization (ISRU) techniques. The most abundant raw material on the Moon is lunar regolith, which, however, is very scarce on Earth, making the study of simulants a necessity. The objective of this study is to characterize and investigate the sintering behavior of EAC-1A lunar regolith simulant. The characterization of the simulant included the determination of the phase assemblage, characteristic temperatures determination and water content analysis. The results are discussed in the context of sintering experiments of EAC-1A simulant, which showed that the material can be sintered to a relative density close to 90%, but only within a very narrow range of temperatures (20–30 °C). Sintering experiments were performed for sieved and unsieved, as well as for dried and non-dried specimens of EAC-1A. In addition, an analysis of the densification and mechanical properties of the sintered specimens was done. The sintering experiments at different temperatures showed that the finest fraction of sieved simulant can reach a higher maximum sintering temperature, and consequently a higher densification and biaxial strength. The non-dried powder exhibited higher densification and biaxial strength after sintering compared to the dried specimen. This difference was explained with a higher green density of the non-dried powder during pressing, rather than due to an actual influence on the sintering mechanism. Nevertheless, drying the powder prior to sintering is important to avoid the overestimation of the strength of specimens to be fabricated on the Moon.
Mortars for application on concrete, e.g. repair mortars or protective coatings, need to have a durable bond to the substrate. This bond is determined by the adhesion between the two materials and by the differential deformations of the mortar and the substrate. In the present contribution, the hygric deformations (shrinkage/expansion) of novel one-part alkali-activated mortars and their bond to concrete substrates are studied. Shrinkage of the mortars was studied at 50 % r.H., while expansion was studied on mortars stored over an open water surface (> 99% r.H.). The bond behaviour was studied by pull-off tests according to DIN EN 1542 and by optical microscopy.
The alkali-activated mortars exhibit hygric deformations much lower than the deformations of an established, commercial mortar for sewer maintenance that was tested as reference in parallel with the alkali-activated mortars. The bond behaviour of the alkali-activated mortars depends strongly on their mix-design and curing. Optical microscopy showed that in the mortars with lower bond strength, cracks developed in the mortar during curing. Mortars with appropriate mix-design and curing did not exhibit cracking, and their pull-off strength (up to > 3 MPa) conformed to the requirements of relevant standards.
