Acid attack is a complex phenomenon arising in construction industries worldwide as it is responsible for the deterioration of concrete in acidic environments resulting in premature degradation with regard to mass changes, weakening of mechanical properties, and increase in porosity due to calcium leaching. This paper investigates the citric acid resistance of geopolymer composites (GP) and its comparison with conventional concrete system (OPC) in lower and higher concentrations of acid medium. The GP samples displayed increased resistance to citric acid attack than OPC system in terms of mass and strength loss. It was also found that geopolymer mortar made with a blend of ground granulated blast furnace slag (GGBS) and red mud (RM) offered increased acid resistance based on the parameters studied in the degradation kinetics

Patients with autoimmune rheumatic diseases with a previous infection by the SARS-CoV-2 virus have exaggerated responses to a single dose of COVID-19 vaccination as compared to fully vaccinated infection naive patients. The second dose is currently recommended at an extended gap after the infection, but the information available regarding response to the second dose in this subgroup is limited. Patients with AIRDs previously infected with COVID-19, who have received at least one dose of AZD1222/ChAdOx1 (n = 200) were included and stratified based on vaccine doses (V), and infection (I) into I + V, I + V + V, V + I, V + V + I. Anti-RBD (receptor binding domain) antibodies were compared across the four groups. In 49 patients of the I + V + V group (AZD12222), paired sera were compared for antibody levels and neutralization after each vaccine dose. Thirty patients with hybrid immunity after BBV152 and 25 with complete vaccination without infection were included as controls. The highest anti-RBD antibody levels were observed in the V + V + I group (18,219 ± 7702 IU/ml) with statistically similar titers in the I + V + V (10,392 ± 8514 IU/ml) and the I + V (8801 ± 8122 IU/ml). This was confirmed in the 49 paired samples that paradoxically showed a lowering of antibody titers after the second dose [9626 (IQR: 4575-18,785)-5781 (2484-11,906); p < 0.001]. Neutralization of the Delta variant was unaffected but Omicron neutralization was significantly reduced after the second dose [45.7 (5.3-86.53)-35% (7.3-70.9); p = 0.028]. Ancillary analyses showed that only the hybrid immune sera could neutralize the Omicron variant and AZD1222 hybrids performed better than BBV152 hybrids. The second dose of AZD1222 did not boost antibody titers in patients with RD who had COVID-19 previously. In the analysis of paired sera, the second dose led to a statistically significant reduction in antibody titers and also reduced neutralization of the Omicron variant.

Background Data on the effectiveness of SARS-CoV-2 vaccines and the durability of protection against the prevalent Omicron variant are scarce, especially in patients with autoimmune rheumatic diseases (AIRDs). Hence, we prospectively studied Omicron breakthrough infections in patients with AIRDs and attempted to isolate associated risk factors. Methods Patients with AIRDs who had completed primary vaccination with either AZD1222 or BBV152 vaccines were included and prospectively followed up from January 2022 onwards for the development of breakthrough Omicron infections. The time interval from the last event [2nd dose of vaccination (V) or past COVID-19 infection (I) whichever was later] to Omicron infection was recorded. Patients were divided based on the events and their order of occurrence into V + V, V + I, I + V, V + I + V, and V + V + I groups. The incidence of breakthrough infections and their predictors were studied with a focus on the vaccine type and hybrid (H) immunity (vaccinated individuals with a history of COVID-19 infection). Results We included 907 patients with AIRDs (53.5 ± 11.7 years and a male-to-female ratio of 1:5.1), and the majority of patients had received AZD1222 (755, 83.2%). Breakthrough infections were observed in 158 of 907(17.4%) of which 97 (10.4%) were confirmed by RT-PCR. Breakthrough infections were significantly greater in the V versus the H group (15.7% and 3.5%, log-rank test, p =  < 0.01). Among the hybrid group, the order of infection and vaccination had no bearing on the risk of breakthrough infections. On multivariate analysis, breakthrough infections were significantly lesser in the H versus the V group [HR: 0.2(0.1–0.4); p = 0.01]. Conclusion The risk of breakthrough Omicron infections in fully vaccinated patients with AIRDs was 17.4% with a significantly lower risk in patients with hybrid immunity.