*5.2. Effect of Waste Wood Ash (WWA) on the Durability Characteristics of Concrete* 5.2.1. Acid Resistance Test

Dashibil and Udoeyo (2002) [81] examined the capability of waste wood ash concrete to withstand acid tests. Two groups of samples had a similar content of aggregates, water, and binder. The only difference was that the first group had only cement as the primary binder and the other group had 15% waste wood ash as a fractional binder substitute. The concrete samples were dipped in strong acid (sulfuric acid) for 54 days. It was revealed that concrete samples that had waste wood ash had a less decrease in their mass loss in comparison to concrete with no waste wood ash at all.

Ejeh and Elinwa (2004) [82] investigated the impact of adding WWA in samples for acid tests against the possibility of corrosion. Two sorts of acids were tried; one was sulfuric acid and the other was nitric acid at 20% concentration. One group of samples had 10% WWA utilized as a fractional binder substitute and the other group of samples was the same as the previous mixes but without WWA. Both groups of samples were dipped in both sorts of acids for 35 days. It was noticed that, in samples with 10% WWA, their resistance to nitric acid was much more enhanced because the loss in mass was lower in comparison to the samples with no WWA, as shown in Figure 1. However, samples with 10% WWA had less resistance to sulfuric acid in comparison to samples with no WWA. This is because of a higher loss in the weight of 10% WWA concrete in comparison to the control sample when dipped in 20% H2SO4, as shown in Figure 2.

**Figure 1.** Change in concrete mass with a period of dipping samples in nitric acid (data from reference [82]).

**Figure 2.** Change in concrete mass with a period of dipping samples in sulfuric acid (data from reference [82]).

### 5.2.2. Water Absorption

Ejeh and Elinwa (2004) [82] inspected the influence of the inclusion of WWA as a fractional binder substitute in mortar blends on the properties of water absorption. Two groups of mortars were developed with similar mixing content except for cement; one blend had only cement as a binder and the other one had 15% WWA as a fractional substitute of cement in the blend. It was revealed that the addition of WWA as a binder substitute at 15% of cement weight assisted in decreasing the water absorption of the developed blends. The mean water absorption of the blends with 15% WWA and no WWA proportions were noted to be 0.75% and 1.30%, correspondingly, but both of the blends were still lower than 10% of the highest water absorption criteria.

Udoeyo et al. (2006) [67] studied the characteristics of water absorption with WWA as a fractional binder substitute material. Sample blends with proportions of WWA ranging from 5 to 30% at an interval of 5% were developed to evaluate the water absorption properties. The water absorption of the sample with WWA as a fractional binder substitute was noted to rise steadily from 0.15 to 1.10% with a rise in the proportion of binder substitution from 5% to 30%, as displayed in Figure 3. At proportions of binder substitution by WWA up to 30%, the developed sample had still reasonable values of water absorption under 10%, which is a tolerable criterion for all of the materials that are used for construction.

**Figure 3.** Co-relation of water with WWA in concrete (data from reference [82]).

#### 5.2.3. Permeability of Chloride Test

Wang et al. (2008) [83] examined the resistance against the permeability of chloride of air entrained in the sample with a fractional substitution of the binder with wood/coal fly ash (WCFA) and wood fly ash (WFA). Proportions of binder substitution by different sorts of FA were utilized as a fractional substitution of binder, such as Class F fly ash, class C fly as, ash from the combusted wood, and coal fly ash. All the concrete specimens were placed in water for 56 days before placing in the chloride permeability test, and the chloride permeability test was conducted per ASTM C 1202 [84]. From the test outcome, it was revealed that the inclusion of WWA at a 25% substitution of cement in the sample had no adverse effect from the chloride on the concrete. The usage of class F/coal mixed and wood ash in fractional replacement of cement had considerable help in dropping the permeability of chloride property of the sample. A minor rise in the permeability of chloride in the sample mix with 25% WWA as cement substitute was noted in comparison to the control sample, perhaps ascribed to the coarse size of WWA particles (30 to 130 microns).

Horsakulthai et al. (2010) [73] investigated the impact of adding very fine ash from the combustion of rice husk, wood, and sugarcane waste from bagasse as a fractional binder substitute on the permeability of chloride of a developed blend of concrete. To assess the concrete permeability of chloride, an accelerated salt ponding technique was utilized for two distinct grades of concrete (grades 20 and 35) developed by the inclusion of ash from rice husk, wood, and bagasse at cement substitution proportions of 0, 10, 20, and 40% of cement weight. The test outcome revealed that the inclusion of fine size ash from rice husk, wood, and bagasse as a fractional replacement of binder in the sample led to the improvement in permeability against chloride and also reduced the coefficient of chloride diffusion. The existence of fine size ash from rice husk, wood, and bagasse in a blend at binder substitutions of 10, 20, and 40% caused a decrease in the coefficient of chloride diffusion by 35–45%, 65–75%, and 80% correspondingly, as compared to the reference mix with only Portland cement as a binder. The inclination of a steady decrease in the coefficient of chloride diffusion for the two distinct grades of concrete was evaluated. The raising dose of binder substitution by ash from rice husk, wood, and bagasse is displayed in Figure 4. The term "PC" in Figure 4 denotes plain concrete; BRWA denotes co-combination of bagasse, rice and waste wood ash; and the numbers after them denotes their percentage added in the mix.

**Figure 4.** Coefficient of the chloride diffusion of samples at 28 days (data from reference [82]).

#### 5.2.4. Alkali Silica Reaction (ASR)

Baxter and Wang (2007) [85] studied the conduct of expansion in mortar blends due to ASR comprising an opal aggregate, which is a very reactive, highly alkaline cement, and three distinct sorts of fly ash (FA). The different sorts of FA were acquired from heating the class C coal. Four groups of mortar blends with the same proportions of ingredients were arranged. The first group of mortar had only Portland cement as a binder and the remaining three groups of mortar blend had three distinct sorts of FA utilized at a uniform dose of binder substitution with 35% of cement by weight. The test outcome revealed that coal fly ash had a higher quantity of alkaline matter as compared to class C FA. The utilization of coal FA in the blend of mortar was revealed to be capable of decreasing the expansion of the alkali-silica reaction at 180 days under 0.1% (highest expansion stated by ASTM C33) from 0.27%. This happened with the reference blend of mortar having Portland cement as the only binder. Between the different sorts of fly ash that were tested, coal fly ash was revealed to have optimal behavior in the mitigating expansion of the alkali-silica reaction.
