Study on the activation of calcined kaolin

Calcined temperature is a key factor to the activity of metakaolin. Structure characteristics and alkali activation of kaolin and its calcined products at different temperatures were analyzed by X-ray diffraction (XRD), nuclear magnetic resonance (NMR), infrared spectrometry (IR) and isothermal calorimetry. The results show that the activity of kaolin calcined at 900°C is best. The characteristic absorption peak of kaolin disappears, a large amount of Al atoms convert from 6-coordination to 5-coordination; some characteristic vibration peaks of kaolin disappear while characteristic absorption peaks of metakaolin appear; There is much heat evolution after mixing it with alkali and the compressive strength is the highest. The strength of samples cured at 80°C for 3 days and 7 days reaches 33.8 and 35.3 MPa respectively

Study on Preparation and Rheological Properties of 3D Printed Pre-Foaming Concrete

The high fluidity and low yield stress of fresh foam concrete affect the shape stability and buildability of foam concrete in the printing process, which is quite a challenge to its application in digital construction. Therefore, this article proposes the preparation and characteristics of 3D printed pre-foaming concrete (3DFC). The rheological properties proved that the addition of 0.1 wt.% Hydroxypropyl methyl cellulose (HPMC) to 3DFCs weakens the fluidity but increases the static yield stress and apparent viscosity, thus enhancing the buildability. More importantly, the influences of surfactant on the rheological property, compressive strength, pore structure and thermal conductivity of 3DFCs were evaluated. Analysis results show that the static yield stress of 3DFCs decreases from 1735 to 687 Pa with surfactant dosage from 0 to 2 wt.%. Moreover, the addition of surfactant significantly reduced the apparent viscosity of 3DFCs (especially at low shear rates), but its viscosity recovery rate was basically unchanged, which is good for buildability. Thanks to the increase of porosity, the volume density of 3DFCs decreased from 2211 to 1159 kg/m3, but the compressive strength of 3DFCs also decreased slightly. The thermal conductivity of 3DFCs shows good thermal insulation performance in the range of 0.2254–0.2879 W/m·K, which is also due to the increase in porosity of 3DFCs. Finally, in order to verify the practical application value of 3DFCs, an industrial printing product with more than 30 layers during the field application is displayed

Activating process of geopolymer source material: kaolinite

The calcining process was recorded by differential scanning calorimetry and thermogravimetry (DSC-TG). The dehydroxylation (activating process) was partitioned into two steps by calculating and comparing the O—H bond lengths between inner hydroxyl group and surface hydroxyl group, as well as the ionic bond of Al—OH and position of —OH. X-ray diffraction (XRD) and compressive strength measurement show that the activity of calcined materials increases with the increasing of temperature in dehydroxylation region but decreases abruptly in the 'spine' region. The suggested temperature for activating kaolinite is 900 ℃

Preparation and mechanical properties of polypropylene fiber reinforced calcined kaolin-fly ash based geopolymer

To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3% (mass fraction) fly ash by steam curing at 80°C for 6d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness

Using Alkali-Activated Cementitious Materials to Solidify High Organic Matter Content Dredged Sludge as Roadbed Material

It is difficult to treat dredged sludge with high organic matter content by solidification. A new solidification of dredged sludge with high organic matter content was developed, using cement, fly ash, slag, and phosphogypsum as a solidifier and strong oxidant KMnO4 and GH as additives, to improve the engineering performance of dredged sludge and make it as a roadbed material possible. The properties of the solidified samples were determined in terms of unconfined compressive strength, products of hydration, toxicity characteristics, water stability, freeze-thaw resistance, and volume stability. The microstructure and hydration products of the dredged sludge after solidification were evaluated by X-ray diffraction analysis, scanning electron microscopy, and thermogravimetry-differential scanning calorimetry analysis. Experimental results showed that the strength of the solidified samples has been significantly improved after treatment by strong oxidants. The effect of GH is better than that of KMnO4. Hydration products (ettringite) were well formed. After solidification by using the binders and strong oxidant GH, the samples had sufficient strength and good water stability performance, freeze-thaw resistance performance, and volume stability performance. The leach liquid of the dredged sludge solidified body meets the standard requirements. So, the dredged sludge after solidification can reach the requirement of the roadbed material