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This article analyzes the integrated effect of industrial by-products (spent fluidized bed catalytic cracking catalyst waste (FCCCw) and paper sludge waste (PSw) generated in paper manufacturing) combined with nano-SiO2 (NS) on the properties of cement binder, when a certain part of the binder is replaced with the said by-products in the cement mix. Standard testing methods were used to analyze the physical and mechanical properties of cement-based materials. For structure analysis, we used X-ray diffraction (XRD), derivative thermogravimetry (DTG), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). It was found that the replacement of cement by a combined additive of FCCCw, PSw and NS is important not only for ecological reasons (abatement of CO2 emissions and recovery of waste through secondary raw materials), but also in order to enhance the properties of cement-based binders. Presumably, higher amounts of calcium silicate hydrate (CSH) and calcium alumina silicate hydrate (CASH) in the compound binder are the result of the low content of portlandite and alite in the test specimens. The specimens modified with all three additives had the highest density (~2100 kg/m3), ultrasonic pulse velocity (UPV) (~4160 m/s) and compressive strength (~105 MPa), which was ~40% higher than in the control specimens. The average pore diameter of the complex binder decreased by 21%, whereas the median pore diameter decreased by 47%.

Pervious concrete (PCO) has many advantages and applications, such as water pooling reduction, noise attenuation, replenishment of groundwater reserves, etc. However, the use of pervious concrete is limited due to its low compressive strength and durability, especially as a result of portlandite leaching from concrete exposed to flowing water. The effects of active additives (nano SiO2 (NS) spent catalyst generated at the fluid catalytic cracking unit (FCCCw) and paper sludge waste burned at 700 °C (PSw)) along with particle size distribution of the coarse aggregate on the properties and durability of pervious concrete were determined in the research. Active additives used in the binder were found to reduce portlandite leaching from concrete exposed to flowing water to significantly increase the resistance of concrete to freezing and thawing cycles and to increase sound absorption, compressive strength and infiltration rate. In addition, industrial waste (FCCCw and PSw) used as active additives significantly reduced the use of clinker in concrete applied in the construction of water pervious systems. The coarse aggregate size distribution had the greatest effect on the density, ultrasound pulse velocity (UPV), porosity, compressive strength and infiltration rate of pervious concrete.

The paper production is developed throughout the world, therefore, more paper sludge waste (PSw) is accumulating. The aim of this work was to determine the properties of PSw burned at 900 °C and its impact on physical–mechanical properties of cementitious matrix and evaluate its usage/utilization possibilities in cementitious materials. For the implementation of the aim, cement-based specimens were prepared and their –mechanical properties were determined. Specimens from five compositions were formed, with 2.5%, 5%, 7.5%, and 10% of the cement by weight replaced with PSw. When 5% of the cement was replaced with PSw, the compressive strength increased by approximately 7%, although density and ultrasound velocity slightly decreased (up to 1.5%). When 7.5% PSw was added, the compressive strength of the specimens decreased. To summarize, it can be stated that up to 5% PSw may be utilized/used for the preparation of cementitious mixtures. The usage of the waste allows environment conservation, reduced amount of cement in mixtures, and improvement of properties of cementitious materials.

After analysis of calorimetric tests results of the cement mixtures with PSw prepared at different temperatures and SEM, XRD, physical-mechanical properties results of cement stone hardened for 7 and 28 days, it is determined that PSw can be utilized/used for the preparation of cement mixtures by adding up to 5%. Depending on the environmental working conditions, the preparation of PSw can be selected. To slow down cement hydration processes, it is useful to use only dried PSw, which slows down the hydration of the cement due to the high content of cellulose contained in PSw. To accelerate cement hydration, it is expedient to use PSw which is burned at 700°C. Dried PSw performs an extended induction hydration period and significantly delays the second heat release time. After the addition of 5% dried PSw, the phase III effect time compared to the control sample is 1.8 h, and after 10% addition, it is extended to 4.4 h. After the addition of 5% burnt PSw, the phase III effect time compared to the control sample is hastened to 1.9 h, after inserting 10% – to 2.4 h. The use of PSw saves the environment, reduces the amount of cement in the mixture and improves the properties of cement materials. Using 5% PSw burned at 700°C instead of cement increases the compressive strength of the specimens, and the density as well as ultrasound pulse velocity values are slightly changed compared to the control sample. It is determined that burnt PSw significantly changes mineral composition and structure. It is found that the microstructure of samples without PSw and samples with dried 5% PSw is similar, crystals formed are visible. With a higher (10%) amount of dried PSw, the microstructure of the cement stone differs significantly from the control samples. Larger voids with plenty of etringite are also visible, as well as higher levels of calcite. The microstructure of specimens with burnt PSw is significantly denser. XRD studies show that with a higher amount of PSw burned at 75°C, the main peak intensities of crystallohydrates ettringite and portlandite are lower, while the peak intensities of calcite are higher compared to samples without PSw. By increasing the amount of dried PSw in mixtures and reducing the amount of cement, the peak intensities corresponding to CSH and CASH are lower compared to those of the control samples. Using burnt PSw also reduces the peak intensities of ettringite, portlandite, CSH and belite, but significantly increases peak intensities of calcite and CASH.